9 files changed, 992 insertions, 0 deletions
diff --git a/devtools/shared/worker/helper.js b/devtools/shared/worker/helper.js
new file mode 100644
index 000000000..69512550b
--- /dev/null
+++ b/devtools/shared/worker/helper.js
@@ -0,0 +1,133 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+(function (root, factory) {
+  "use strict";
+
+  if (typeof define === "function" && define.amd) {
+    define(factory);
+  } else if (typeof exports === "object") {
+    module.exports = factory();
+  } else {
+    root.workerHelper = factory();
+  }
+}(this, function () {
+  "use strict";
+
+  /**
+   * This file is to only be included by ChromeWorkers. This exposes
+   * a `createTask` function to workers to register tasks for communication
+   * back to `devtools/shared/worker`.
+   *
+   * Tasks can be send their responses via a return value, either a primitive
+   * or a promise.
+   *
+   * createTask(self, "average", function (data) {
+   *   return data.reduce((sum, val) => sum + val, 0) / data.length;
+   * });
+   *
+   * createTask(self, "average", function (data) {
+   *   return new Promise((resolve, reject) => {
+   *     resolve(data.reduce((sum, val) => sum + val, 0) / data.length);
+   *   });
+   * });
+   *
+   *
+   * Errors:
+   *
+   * Returning an Error value, or if the returned promise is rejected, this
+   * propagates to the DevToolsWorker as a rejected promise. If an error is
+   * thrown in a synchronous function, that error is also propagated.
+   */
+
+  /**
+   * Takes a worker's `self` object, a task name, and a function to
+   * be called when that task is called. The task is called with the
+   * passed in data as the first argument
+   *
+   * @param {object} self
+   * @param {string} name
+   * @param {function} fn
+   */
+  function createTask(self, name, fn) {
+    // Store a hash of task name to function on the Worker
+    if (!self._tasks) {
+      self._tasks = {};
+    }
+
+    // Create the onmessage handler if not yet created.
+    if (!self.onmessage) {
+      self.onmessage = createHandler(self);
+    }
+
+    // Store the task on the worker.
+    self._tasks[name] = fn;
+  }
+
+  /**
+   * Creates the `self.onmessage` handler for a Worker.
+   *
+   * @param {object} self
+   * @return {function}
+   */
+  function createHandler(self) {
+    return function (e) {
+      let { id, task, data } = e.data;
+      let taskFn = self._tasks[task];
+
+      if (!taskFn) {
+        self.postMessage({ id, error: `Task "${task}" not found in worker.` });
+        return;
+      }
+
+      try {
+        let results;
+        handleResponse(taskFn(data));
+      } catch (e) {
+        handleError(e);
+      }
+
+      function handleResponse(response) {
+        // If a promise
+        if (response && typeof response.then === "function") {
+          response.then(val => self.postMessage({ id, response: val }), handleError);
+        }
+        // If an error object
+        else if (response instanceof Error) {
+          handleError(response);
+        }
+        // If anything else
+        else {
+          self.postMessage({ id, response });
+        }
+      }
+
+      function handleError(error = "Error") {
+        try {
+          // First, try and structured clone the error across directly.
+          self.postMessage({ id, error });
+        } catch (_) {
+          // We could not clone whatever error value was given. Do our best to
+          // stringify it.
+          let errorString = `Error while performing task "${task}": `;
+
+          try {
+            errorString += error.toString();
+          } catch (_) {
+            errorString += "<could not stringify error>";
+          }
+
+          if ("stack" in error) {
+            try {
+              errorString += "\n" + error.stack;
+            } catch (_) { }
+          }
+
+          self.postMessage({ id, error: errorString });
+        }
+      }
+    };
+  }
+
+  return { createTask: createTask };
+}.bind(this)));
diff --git a/devtools/shared/worker/loader.js b/devtools/shared/worker/loader.js
new file mode 100644
index 000000000..1de72963d
--- /dev/null
+++ b/devtools/shared/worker/loader.js
@@ -0,0 +1,517 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+// A CommonJS module loader that is designed to run inside a worker debugger.
+// We can't simply use the SDK module loader, because it relies heavily on
+// Components, which isn't available in workers.
+//
+// In principle, the standard instance of the worker loader should provide the
+// same built-in modules as its devtools counterpart, so that both loaders are
+// interchangable on the main thread, making them easier to test.
+//
+// On the worker thread, some of these modules, in particular those that rely on
+// the use of Components, and for which the worker debugger doesn't provide an
+// alternative API, will be replaced by vacuous objects. Consequently, they can
+// still be required, but any attempts to use them will lead to an exception.
+
+this.EXPORTED_SYMBOLS = ["WorkerDebuggerLoader", "worker"];
+
+// Some notes on module ids and URLs:
+//
+// An id is either a relative id or an absolute id. An id is relative if and
+// only if it starts with a dot. An absolute id is a normalized id if and only
+// if it contains no redundant components.
+//
+// Every normalized id is a URL. A URL is either an absolute URL or a relative
+// URL. A URL is absolute if and only if it starts with a scheme name followed
+// by a colon and 2 or 3 slashes.
+
+/**
+ * Convert the given relative id to an absolute id.
+ *
+ * @param String id
+ *        The relative id to be resolved.
+ * @param String baseId
+ *        The absolute base id to resolve the relative id against.
+ *
+ * @return String
+ *         An absolute id
+ */
+function resolveId(id, baseId) {
+  return baseId + "/../" + id;
+}
+
+/**
+ * Convert the given absolute id to a normalized id.
+ *
+ * @param String id
+ *        The absolute id to be normalized.
+ *
+ * @return String
+ *         A normalized id.
+ */
+function normalizeId(id) {
+  // An id consists of an optional root and a path. A root consists of either
+  // a scheme name followed by 2 or 3 slashes, or a single slash. Slashes in the
+  // root are not used as separators, so only normalize the path.
+  let [_, root, path] = id.match(/^(\w+:\/\/\/?|\/)?(.*)/);
+
+  let stack = [];
+  path.split("/").forEach(function (component) {
+    switch (component) {
+      case "":
+      case ".":
+        break;
+      case "..":
+        if (stack.length === 0) {
+          if (root !== undefined) {
+            throw new Error("Can't normalize absolute id '" + id + "'!");
+          } else {
+            stack.push("..");
+          }
+        } else {
+          if (stack[stack.length - 1] == "..") {
+            stack.push("..");
+          } else {
+            stack.pop();
+          }
+        }
+        break;
+      default:
+        stack.push(component);
+        break;
+    }
+  });
+
+  return (root ? root : "") + stack.join("/");
+}
+
+/**
+ * Create a module object with the given normalized id.
+ *
+ * @param String
+ *        The normalized id of the module to be created.
+ *
+ * @return Object
+ *         A module with the given id.
+ */
+function createModule(id) {
+  return Object.create(null, {
+    // CommonJS specifies the id property to be non-configurable and
+    // non-writable.
+    id: {
+      configurable: false,
+      enumerable: true,
+      value: id,
+      writable: false
+    },
+
+    // CommonJS does not specify an exports property, so follow the NodeJS
+    // convention, which is to make it non-configurable and writable.
+    exports: {
+      configurable: false,
+      enumerable: true,
+      value: Object.create(null),
+      writable: true
+    }
+  });
+}
+
+/**
+ * Create a CommonJS loader with the following options:
+ * - createSandbox:
+ *     A function that will be used to create sandboxes. It should take the name
+ *     and prototype of the sandbox to be created, and return the newly created
+ *     sandbox as result. This option is required.
+ * - globals:
+ *     A map of names to built-in globals that will be exposed to every module.
+ *     Defaults to the empty map.
+ * - loadSubScript:
+ *     A function that will be used to load scripts in sandboxes. It should take
+ *     the URL from and the sandbox in which the script is to be loaded, and not
+ *     return a result. This option is required.
+ * - modules:
+ *     A map from normalized ids to built-in modules that will be added to the
+ *     module cache. Defaults to the empty map.
+ * - paths:
+ *     A map of paths to base URLs that will be used to resolve relative URLs to
+ *     absolute URLS. Defaults to the empty map.
+ * - resolve:
+ *     A function that will be used to resolve relative ids to absolute ids. It
+ *     should take the relative id of a module to be required and the absolute
+ *     id of the requiring module as arguments, and return the absolute id of
+ *     the module to be required as result. Defaults to resolveId above.
+ */
+function WorkerDebuggerLoader(options) {
+  /**
+   * Convert the given relative URL to an absolute URL, using the map of paths
+   * given below.
+   *
+   * @param String url
+   *        The relative URL to be resolved.
+   *
+   * @return String
+   *         An absolute URL.
+   */
+  function resolveURL(url) {
+    let found = false;
+    for (let [path, baseURL] of paths) {
+      if (url.startsWith(path)) {
+        found = true;
+        url = url.replace(path, baseURL);
+        break;
+      }
+    }
+    if (!found) {
+      throw new Error("Can't resolve relative URL '" + url + "'!");
+    }
+
+    // If the url has no extension, use ".js" by default.
+    return url.endsWith(".js") ? url : url + ".js";
+  }
+
+  /**
+   * Load the given module with the given url.
+   *
+   * @param Object module
+   *        The module object to be loaded.
+   * @param String url
+   *        The URL to load the module from.
+   */
+  function loadModule(module, url) {
+    // CommonJS specifies 3 free variables: require, exports, and module. These
+    // must be exposed to every module, so define these as properties on the
+    // sandbox prototype. Additional built-in globals are exposed by making
+    // the map of built-in globals the prototype of the sandbox prototype.
+    let prototype = Object.create(globals);
+    prototype.Components = {};
+    prototype.require = createRequire(module);
+    prototype.exports = module.exports;
+    prototype.module = module;
+
+    let sandbox = createSandbox(url, prototype);
+    try {
+      loadSubScript(url, sandbox);
+    } catch (error) {
+      if (/^Error opening input stream/.test(String(error))) {
+        throw new Error("Can't load module '" + module.id + "' with url '" +
+                        url + "'!");
+      }
+      throw error;
+    }
+
+    // The value of exports may have been changed by the module script, so
+    // freeze it if and only if it is still an object.
+    if (typeof module.exports === "object" && module.exports !== null) {
+      Object.freeze(module.exports);
+    }
+  }
+
+  /**
+   * Create a require function for the given module. If no module is given,
+   * create a require function for the top-level module instead.
+   *
+   * @param Object requirer
+   *        The module for which the require function is to be created.
+   *
+   * @return Function
+   *         A require function for the given module.
+   */
+  function createRequire(requirer) {
+    return function require(id) {
+      // Make sure an id was passed.
+      if (id === undefined) {
+        throw new Error("Can't require module without id!");
+      }
+
+      // Built-in modules are cached by id rather than URL, so try to find the
+      // module to be required by id first.
+      let module = modules[id];
+      if (module === undefined) {
+        // Failed to find the module to be required by id, so convert the id to
+        // a URL and try again.
+
+        // If the id is relative, convert it to an absolute id.
+        if (id.startsWith(".")) {
+          if (requirer === undefined) {
+            throw new Error("Can't require top-level module with relative id " +
+                            "'" + id + "'!");
+          }
+          id = resolve(id, requirer.id);
+        }
+
+        // Convert the absolute id to a normalized id.
+        id = normalizeId(id);
+
+        // Convert the normalized id to a URL.
+        let url = id;
+
+        // If the URL is relative, resolve it to an absolute URL.
+        if (url.match(/^\w+:\/\//) === null) {
+          url = resolveURL(id);
+        }
+
+        // Try to find the module to be required by URL.
+        module = modules[url];
+        if (module === undefined) {
+          // Failed to find the module to be required in the cache, so create
+          // a new module, load it from the given URL, and add it to the cache.
+
+          // Add modules to the cache early so that any recursive calls to
+          // require for the same module will return the partially-loaded module
+          // from the cache instead of triggering a new load.
+          module = modules[url] = createModule(id);
+
+          try {
+            loadModule(module, url);
+          } catch (error) {
+            // If the module failed to load, remove it from the cache so that
+            // subsequent calls to require for the same module will trigger a
+            // new load, instead of returning a partially-loaded module from
+            // the cache.
+            delete modules[url];
+            throw error;
+          }
+
+          Object.freeze(module);
+        }
+      }
+
+      return module.exports;
+    };
+  }
+
+  let createSandbox = options.createSandbox;
+  let globals = options.globals || Object.create(null);
+  let loadSubScript = options.loadSubScript;
+
+  // Create the module cache, by converting each entry in the map from
+  // normalized ids to built-in modules to a module object, with the exports
+  // property of each module set to a frozen version of the original entry.
+  let modules = options.modules || {};
+  for (let id in modules) {
+    let module = createModule(id);
+    module.exports = Object.freeze(modules[id]);
+    modules[id] = module;
+  }
+
+  // Convert the map of paths to base URLs into an array for use by resolveURL.
+  // The array is sorted from longest to shortest path to ensure that the
+  // longest path is always the first to be found.
+  let paths = options.paths || Object.create(null);
+  paths = Object.keys(paths)
+                .sort((a, b) => b.length - a.length)
+                .map(path => [path, paths[path]]);
+
+  let resolve = options.resolve || resolveId;
+
+  this.require = createRequire();
+}
+
+this.WorkerDebuggerLoader = WorkerDebuggerLoader;
+
+// The following APIs rely on the use of Components, and the worker debugger
+// does not provide alternative definitions for them. Consequently, they are
+// stubbed out both on the main thread and worker threads.
+
+var chrome = {
+  CC: undefined,
+  Cc: undefined,
+  ChromeWorker: undefined,
+  Cm: undefined,
+  Ci: undefined,
+  Cu: undefined,
+  Cr: undefined,
+  components: undefined
+};
+
+var loader = {
+  lazyGetter: function (object, name, lambda) {
+    Object.defineProperty(object, name, {
+      get: function () {
+        delete object[name];
+        return object[name] = lambda.apply(object);
+      },
+      configurable: true,
+      enumerable: true
+    });
+  },
+  lazyImporter: function () {
+    throw new Error("Can't import JSM from worker thread!");
+  },
+  lazyServiceGetter: function () {
+    throw new Error("Can't import XPCOM service from worker thread!");
+  },
+  lazyRequireGetter: function (obj, property, module, destructure) {
+    Object.defineProperty(obj, property, {
+      get: () => destructure ? worker.require(module)[property]
+                             : worker.require(module || property)
+    });
+  }
+};
+
+// The following APIs are defined differently depending on whether we are on the
+// main thread or a worker thread. On the main thread, we use the Components
+// object to implement them. On worker threads, we use the APIs provided by
+// the worker debugger.
+
+var {
+  Debugger,
+  URL,
+  createSandbox,
+  dump,
+  rpc,
+  loadSubScript,
+  reportError,
+  setImmediate,
+  xpcInspector
+} = (function () {
+  if (typeof Components === "object") { // Main thread
+    let {
+      Constructor: CC,
+      classes: Cc,
+      manager: Cm,
+      interfaces: Ci,
+      results: Cr,
+      utils: Cu
+    } = Components;
+
+    let principal = CC("@mozilla.org/systemprincipal;1", "nsIPrincipal")();
+
+    // To ensure that the this passed to addDebuggerToGlobal is a global, the
+    // Debugger object needs to be defined in a sandbox.
+    let sandbox = Cu.Sandbox(principal, {});
+    Cu.evalInSandbox(
+      "Components.utils.import('resource://gre/modules/jsdebugger.jsm');" +
+      "addDebuggerToGlobal(this);",
+      sandbox
+    );
+    let Debugger = sandbox.Debugger;
+
+    let createSandbox = function (name, prototype) {
+      return Cu.Sandbox(principal, {
+        invisibleToDebugger: true,
+        sandboxName: name,
+        sandboxPrototype: prototype,
+        wantComponents: false,
+        wantXrays: false
+      });
+    };
+
+    let rpc = undefined;
+
+    let subScriptLoader = Cc["@mozilla.org/moz/jssubscript-loader;1"].
+                 getService(Ci.mozIJSSubScriptLoader);
+
+    let loadSubScript = function (url, sandbox) {
+      subScriptLoader.loadSubScript(url, sandbox, "UTF-8");
+    };
+
+    let reportError = Cu.reportError;
+
+    let Timer = Cu.import("resource://gre/modules/Timer.jsm", {});
+
+    let setImmediate = function (callback) {
+      Timer.setTimeout(callback, 0);
+    };
+
+    let xpcInspector = Cc["@mozilla.org/jsinspector;1"].
+                       getService(Ci.nsIJSInspector);
+
+    return {
+      Debugger,
+      URL: this.URL,
+      createSandbox,
+      dump: this.dump,
+      rpc,
+      loadSubScript,
+      reportError,
+      setImmediate,
+      xpcInspector
+    };
+  } else { // Worker thread
+    let requestors = [];
+
+    let scope = this;
+
+    let xpcInspector = {
+      get eventLoopNestLevel() {
+        return requestors.length;
+      },
+
+      get lastNestRequestor() {
+        return requestors.length === 0 ? null : requestors[requestors.length - 1];
+      },
+
+      enterNestedEventLoop: function (requestor) {
+        requestors.push(requestor);
+        scope.enterEventLoop();
+        return requestors.length;
+      },
+
+      exitNestedEventLoop: function () {
+        requestors.pop();
+        scope.leaveEventLoop();
+        return requestors.length;
+      }
+    };
+
+    return {
+      Debugger: this.Debugger,
+      URL: this.URL,
+      createSandbox: this.createSandbox,
+      dump: this.dump,
+      rpc: this.rpc,
+      loadSubScript: this.loadSubScript,
+      reportError: this.reportError,
+      setImmediate: this.setImmediate,
+      xpcInspector: xpcInspector
+    };
+  }
+}).call(this);
+
+// Create the default instance of the worker loader, using the APIs we defined
+// above.
+
+this.worker = new WorkerDebuggerLoader({
+  createSandbox: createSandbox,
+  globals: {
+    "isWorker": true,
+    "dump": dump,
+    "loader": loader,
+    "reportError": reportError,
+    "rpc": rpc,
+    "setImmediate": setImmediate,
+    "URL": URL,
+  },
+  loadSubScript: loadSubScript,
+  modules: {
+    "Debugger": Debugger,
+    "Services": Object.create(null),
+    "chrome": chrome,
+    "xpcInspector": xpcInspector
+  },
+  paths: {
+    // ⚠ DISCUSSION ON DEV-DEVELOPER-TOOLS REQUIRED BEFORE MODIFYING ⚠
+    "": "resource://gre/modules/commonjs/",
+    // ⚠ DISCUSSION ON DEV-DEVELOPER-TOOLS REQUIRED BEFORE MODIFYING ⚠
+    // Modules here are intended to have one implementation for
+    // chrome, and a separate implementation for content.  Here we
+    // map the directory to the chrome subdirectory, but the content
+    // loader will map to the content subdirectory.  See the
+    // README.md in devtools/shared/platform.
+    "devtools/shared/platform": "resource://devtools/shared/platform/chrome",
+    // ⚠ DISCUSSION ON DEV-DEVELOPER-TOOLS REQUIRED BEFORE MODIFYING ⚠
+    "devtools": "resource://devtools",
+    // ⚠ DISCUSSION ON DEV-DEVELOPER-TOOLS REQUIRED BEFORE MODIFYING ⚠
+    "promise": "resource://gre/modules/Promise-backend.js",
+    // ⚠ DISCUSSION ON DEV-DEVELOPER-TOOLS REQUIRED BEFORE MODIFYING ⚠
+    "source-map": "resource://devtools/shared/sourcemap/source-map.js",
+    // ⚠ DISCUSSION ON DEV-DEVELOPER-TOOLS REQUIRED BEFORE MODIFYING ⚠
+    "xpcshell-test": "resource://test"
+    // ⚠ DISCUSSION ON DEV-DEVELOPER-TOOLS REQUIRED BEFORE MODIFYING ⚠
+  }
+});
diff --git a/devtools/shared/worker/moz.build b/devtools/shared/worker/moz.build
new file mode 100644
index 000000000..28b26c0a7
--- /dev/null
+++ b/devtools/shared/worker/moz.build
@@ -0,0 +1,13 @@
+# -*- Mode: python; indent-tabs-mode: nil; tab-width: 40 -*-
+# vim: set filetype=python:
+# This Source Code Form is subject to the terms of the Mozilla Public
+# License, v. 2.0. If a copy of the MPL was not distributed with this
+# file, You can obtain one at http://mozilla.org/MPL/2.0/.
+
+BROWSER_CHROME_MANIFESTS += ['tests/browser/browser.ini']
+
+DevToolsModules(
+    'helper.js',
+    'loader.js',
+    'worker.js',
+)
diff --git a/devtools/shared/worker/tests/browser/.eslintrc.js b/devtools/shared/worker/tests/browser/.eslintrc.js
new file mode 100644
index 000000000..698ae9181
--- /dev/null
+++ b/devtools/shared/worker/tests/browser/.eslintrc.js
@@ -0,0 +1,6 @@
+"use strict";
+
+module.exports = {
+  // Extend from the shared list of defined globals for mochitests.
+  "extends": "../../../../.eslintrc.mochitests.js"
+};
diff --git a/devtools/shared/worker/tests/browser/browser.ini b/devtools/shared/worker/tests/browser/browser.ini
new file mode 100644
index 000000000..a64916dff
--- /dev/null
+++ b/devtools/shared/worker/tests/browser/browser.ini
@@ -0,0 +1,9 @@
+[DEFAULT]
+tags = devtools
+subsuite = devtools
+support-files =
+  ../../../../server/tests/browser/head.js
+
+[browser_worker-01.js]
+[browser_worker-02.js]
+[browser_worker-03.js]
diff --git a/devtools/shared/worker/tests/browser/browser_worker-01.js b/devtools/shared/worker/tests/browser/browser_worker-01.js
new file mode 100644
index 000000000..7679e4166
--- /dev/null
+++ b/devtools/shared/worker/tests/browser/browser_worker-01.js
@@ -0,0 +1,45 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// Tests that the devtools/shared/worker communicates properly
+// as both CommonJS module and as a JSM.
+
+const WORKER_URL =
+  "resource://devtools/client/shared/widgets/GraphsWorker.js";
+
+const count = 100000;
+const WORKER_DATA = (function () {
+  let timestamps = [];
+  for (let i = 0; i < count; i++) {
+    timestamps.push(i);
+  }
+  return timestamps;
+})();
+const INTERVAL = 100;
+const DURATION = 1000;
+
+add_task(function* () {
+  // Test both CJS and JSM versions
+
+  yield testWorker("JSM", () => Cu.import("resource://devtools/shared/worker/worker.js", {}));
+  yield testWorker("CommonJS", () => require("devtools/shared/worker/worker"));
+});
+
+function* testWorker(context, workerFactory) {
+  let { DevToolsWorker, workerify } = workerFactory();
+  let worker = new DevToolsWorker(WORKER_URL);
+  let results = yield worker.performTask("plotTimestampsGraph", {
+    timestamps: WORKER_DATA,
+    interval: INTERVAL,
+    duration: DURATION
+  });
+
+  ok(results.plottedData.length,
+    `worker should have returned an object with array properties in ${context}`);
+
+  let fn = workerify(function (x) { return x * x; });
+  is((yield fn(5)), 25, `workerify works in ${context}`);
+  fn.destroy();
+
+  worker.destroy();
+}
diff --git a/devtools/shared/worker/tests/browser/browser_worker-02.js b/devtools/shared/worker/tests/browser/browser_worker-02.js
new file mode 100644
index 000000000..e6a9a54cf
--- /dev/null
+++ b/devtools/shared/worker/tests/browser/browser_worker-02.js
@@ -0,0 +1,46 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// Tests errors are handled properly by the DevToolsWorker.
+
+const { DevToolsWorker } = require("devtools/shared/worker/worker");
+const WORKER_URL =
+  "resource://devtools/client/shared/widgets/GraphsWorker.js";
+
+add_task(function* () {
+  try {
+    let workerNotFound = new DevToolsWorker("resource://i/dont/exist.js");
+    ok(false, "Creating a DevToolsWorker with an invalid URL throws");
+  } catch (e) {
+    ok(true, "Creating a DevToolsWorker with an invalid URL throws");
+  }
+
+  let worker = new DevToolsWorker(WORKER_URL);
+  try {
+    // plotTimestampsGraph requires timestamp, interval an duration props on the object
+    // passed in so there should be an error thrown in the worker
+    let results = yield worker.performTask("plotTimestampsGraph", {});
+    ok(false, "DevToolsWorker returns a rejected promise when an error occurs in the worker");
+  } catch (e) {
+    ok(true, "DevToolsWorker returns a rejected promise when an error occurs in the worker");
+  }
+
+  try {
+    let results = yield worker.performTask("not a real task");
+    ok(false, "DevToolsWorker returns a rejected promise when task does not exist");
+  } catch (e) {
+    ok(true, "DevToolsWorker returns a rejected promise when task does not exist");
+  }
+
+  worker.destroy();
+  try {
+    let results = yield worker.performTask("plotTimestampsGraph", {
+      timestamps: [0, 1, 2, 3, 4, 5, 6, 7, 8, 9],
+      interval: 1,
+      duration: 1
+    });
+    ok(false, "DevToolsWorker rejects when performing a task on a destroyed worker");
+  } catch (e) {
+    ok(true, "DevToolsWorker rejects when performing a task on a destroyed worker");
+  }
+});
diff --git a/devtools/shared/worker/tests/browser/browser_worker-03.js b/devtools/shared/worker/tests/browser/browser_worker-03.js
new file mode 100644
index 000000000..053e381b9
--- /dev/null
+++ b/devtools/shared/worker/tests/browser/browser_worker-03.js
@@ -0,0 +1,52 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// Tests that the devtools/shared/worker can handle:
+// returned primitives (or promise or Error)
+//
+// And tests `workerify` by doing so.
+
+const { DevToolsWorker, workerify } = require("devtools/shared/worker/worker");
+function square(x) {
+  return x * x;
+}
+
+function squarePromise(x) {
+  return new Promise((resolve) => resolve(x * x));
+}
+
+function squareError(x) {
+  return new Error("Nope");
+}
+
+function squarePromiseReject(x) {
+  return new Promise((_, reject) => reject("Nope"));
+}
+
+add_task(function* () {
+  let fn = workerify(square);
+  is((yield fn(5)), 25, "return primitives successful");
+  fn.destroy();
+
+  fn = workerify(squarePromise);
+  is((yield fn(5)), 25, "promise primitives successful");
+  fn.destroy();
+
+  fn = workerify(squareError);
+  try {
+    yield fn(5);
+    ok(false, "return error should reject");
+  } catch (e) {
+    ok(true, "return error should reject");
+  }
+  fn.destroy();
+
+  fn = workerify(squarePromiseReject);
+  try {
+    yield fn(5);
+    ok(false, "returned rejected promise rejects");
+  } catch (e) {
+    ok(true, "returned rejected promise rejects");
+  }
+  fn.destroy();
+});
diff --git a/devtools/shared/worker/worker.js b/devtools/shared/worker/worker.js
new file mode 100644
index 000000000..9ed9afa27
--- /dev/null
+++ b/devtools/shared/worker/worker.js
@@ -0,0 +1,171 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+"use strict";
+
+/* global ChromeWorker */
+
+(function (factory) {
+  if (this.module && module.id.indexOf("worker") >= 0) {
+    // require
+    const { Cc, Ci, Cu, ChromeWorker } = require("chrome");
+    const dumpn = require("devtools/shared/DevToolsUtils").dumpn;
+    factory.call(this, require, exports, module, { Cc, Ci, Cu }, ChromeWorker, dumpn);
+  } else {
+    // Cu.import
+    const { classes: Cc, interfaces: Ci, utils: Cu } = Components;
+    const { require } = Cu.import("resource://devtools/shared/Loader.jsm", {});
+    this.isWorker = false;
+    this.Promise = Cu.import("resource://gre/modules/Promise.jsm", {}).Promise;
+    this.console = Cu.import("resource://gre/modules/Console.jsm", {}).console;
+    factory.call(
+      this, require, this, { exports: this },
+      { Cc, Ci, Cu }, ChromeWorker, null
+    );
+    this.EXPORTED_SYMBOLS = ["DevToolsWorker"];
+  }
+}).call(this, function (require, exports, module, { Ci, Cc }, ChromeWorker, dumpn) {
+  let MESSAGE_COUNTER = 0;
+
+  /**
+   * Creates a wrapper around a ChromeWorker, providing easy
+   * communication to offload demanding tasks. The corresponding URL
+   * must implement the interface provided by `devtools/shared/worker/helper`.
+   *
+   * @see `./devtools/client/shared/widgets/GraphsWorker.js`
+   *
+   * @param {string} url
+   *        The URL of the worker.
+   * @param Object opts
+   *        An option with the following optional fields:
+   *        - name: a name that will be printed with logs
+   *        - verbose: log incoming and outgoing messages
+   */
+  function DevToolsWorker(url, opts) {
+    opts = opts || {};
+    this._worker = new ChromeWorker(url);
+    this._verbose = opts.verbose;
+    this._name = opts.name;
+
+    this._worker.addEventListener("error", this.onError, false);
+  }
+  exports.DevToolsWorker = DevToolsWorker;
+
+  /**
+   * Performs the given task in a chrome worker, passing in data.
+   * Returns a promise that resolves when the task is completed, resulting in
+   * the return value of the task.
+   *
+   * @param {string} task
+   *        The name of the task to execute in the worker.
+   * @param {any} data
+   *        Data to be passed into the task implemented by the worker.
+   * @return {Promise}
+   */
+  DevToolsWorker.prototype.performTask = function (task, data) {
+    if (this._destroyed) {
+      return Promise.reject("Cannot call performTask on a destroyed DevToolsWorker");
+    }
+    let worker = this._worker;
+    let id = ++MESSAGE_COUNTER;
+    let payload = { task, id, data };
+
+    if (this._verbose && dumpn) {
+      dumpn("Sending message to worker" +
+            (this._name ? (" (" + this._name + ")") : "") +
+            ": " +
+            JSON.stringify(payload, null, 2));
+    }
+    worker.postMessage(payload);
+
+    return new Promise((resolve, reject) => {
+      let listener = ({ data: result }) => {
+        if (this._verbose && dumpn) {
+          dumpn("Received message from worker" +
+                (this._name ? (" (" + this._name + ")") : "") +
+                ": " +
+                JSON.stringify(result, null, 2));
+        }
+
+        if (result.id !== id) {
+          return;
+        }
+        worker.removeEventListener("message", listener);
+        if (result.error) {
+          reject(result.error);
+        } else {
+          resolve(result.response);
+        }
+      };
+
+      worker.addEventListener("message", listener);
+    });
+  };
+
+  /**
+   * Terminates the underlying worker. Use when no longer needing the worker.
+   */
+  DevToolsWorker.prototype.destroy = function () {
+    this._worker.terminate();
+    this._worker = null;
+    this._destroyed = true;
+  };
+
+  DevToolsWorker.prototype.onError = function ({ message, filename, lineno }) {
+    dump(new Error(message + " @ " + filename + ":" + lineno) + "\n");
+  };
+
+  /**
+   * Takes a function and returns a Worker-wrapped version of the same function.
+   * Returns a promise upon resolution.
+   * @see `./devtools/shared/shared/tests/browser/browser_devtools-worker-03.js
+   *
+   * ⚠ This should only be used for tests or A/B testing performance ⚠
+   *
+   * The original function must:
+   *
+   * Be a pure function, that is, not use any variables not declared within the
+   * function, or its arguments.
+   *
+   * Return a value or a promise.
+   *
+   * Note any state change in the worker will not affect the callee's context.
+   *
+   * @param {function} fn
+   * @return {function}
+   */
+  function workerify(fn) {
+    console.warn("`workerify` should only be used in tests or measuring performance. " +
+                 "This creates an object URL on the browser window, and should not be " +
+                 "used in production.");
+    // Fetch via window/utils here as we don't want to include
+    // this module normally.
+    let { getMostRecentBrowserWindow } = require("sdk/window/utils");
+    let { URL, Blob } = getMostRecentBrowserWindow();
+    let stringifiedFn = createWorkerString(fn);
+    let blob = new Blob([stringifiedFn]);
+    let url = URL.createObjectURL(blob);
+    let worker = new DevToolsWorker(url);
+
+    let wrapperFn = data => worker.performTask("workerifiedTask", data);
+
+    wrapperFn.destroy = function () {
+      URL.revokeObjectURL(url);
+      worker.destroy();
+    };
+
+    return wrapperFn;
+  }
+  exports.workerify = workerify;
+
+  /**
+   * Takes a function, and stringifies it, attaching the worker-helper.js
+   * boilerplate hooks.
+   */
+  function createWorkerString(fn) {
+    return `importScripts("resource://gre/modules/workers/require.js");
+            const { createTask } = require("resource://devtools/shared/worker/helper.js");
+            createTask(self, "workerifiedTask", ${fn.toString()});`;
+  }
+});