Add m-esr52 at 52.6.0

1 files changed, 901 insertions, 0 deletions

diff --git a/toolkit/components/thumbnails/PageThumbs.jsm b/toolkit/components/thumbnails/PageThumbs.jsm
new file mode 100644
index 000000000..9bd3ae4b3
--- /dev/null
+++ b/toolkit/components/thumbnails/PageThumbs.jsm
@@ -0,0 +1,901 @@
+/* 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";
+
+this.EXPORTED_SYMBOLS = ["PageThumbs", "PageThumbsStorage"];
+
+const Cu = Components.utils;
+const Cc = Components.classes;
+const Ci = Components.interfaces;
+
+const PREF_STORAGE_VERSION = "browser.pagethumbnails.storage_version";
+const LATEST_STORAGE_VERSION = 3;
+
+const EXPIRATION_MIN_CHUNK_SIZE = 50;
+const EXPIRATION_INTERVAL_SECS = 3600;
+
+var gRemoteThumbId = 0;
+
+// If a request for a thumbnail comes in and we find one that is "stale"
+// (or don't find one at all) we automatically queue a request to generate a
+// new one.
+const MAX_THUMBNAIL_AGE_SECS = 172800; // 2 days == 60*60*24*2 == 172800 secs.
+
+/**
+ * Name of the directory in the profile that contains the thumbnails.
+ */
+const THUMBNAIL_DIRECTORY = "thumbnails";
+
+Cu.import("resource://gre/modules/XPCOMUtils.jsm", this);
+Cu.import("resource://gre/modules/PromiseWorker.jsm", this);
+Cu.import("resource://gre/modules/Promise.jsm", this);
+Cu.import("resource://gre/modules/osfile.jsm", this);
+
+Cu.importGlobalProperties(['FileReader']);
+
+XPCOMUtils.defineLazyModuleGetter(this, "NetUtil",
+  "resource://gre/modules/NetUtil.jsm");
+
+XPCOMUtils.defineLazyModuleGetter(this, "Services",
+  "resource://gre/modules/Services.jsm");
+
+XPCOMUtils.defineLazyModuleGetter(this, "FileUtils",
+  "resource://gre/modules/FileUtils.jsm");
+
+XPCOMUtils.defineLazyModuleGetter(this, "PlacesUtils",
+  "resource://gre/modules/PlacesUtils.jsm");
+
+XPCOMUtils.defineLazyServiceGetter(this, "gUpdateTimerManager",
+  "@mozilla.org/updates/timer-manager;1", "nsIUpdateTimerManager");
+
+XPCOMUtils.defineLazyGetter(this, "gCryptoHash", function () {
+  return Cc["@mozilla.org/security/hash;1"].createInstance(Ci.nsICryptoHash);
+});
+
+XPCOMUtils.defineLazyGetter(this, "gUnicodeConverter", function () {
+  let converter = Cc["@mozilla.org/intl/scriptableunicodeconverter"]
+                    .createInstance(Ci.nsIScriptableUnicodeConverter);
+  converter.charset = 'utf8';
+  return converter;
+});
+
+XPCOMUtils.defineLazyModuleGetter(this, "Task",
+  "resource://gre/modules/Task.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "Deprecated",
+  "resource://gre/modules/Deprecated.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "AsyncShutdown",
+  "resource://gre/modules/AsyncShutdown.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "PageThumbUtils",
+  "resource://gre/modules/PageThumbUtils.jsm");
+XPCOMUtils.defineLazyModuleGetter(this, "PrivateBrowsingUtils",
+  "resource://gre/modules/PrivateBrowsingUtils.jsm");
+
+/**
+ * Utilities for dealing with promises and Task.jsm
+ */
+const TaskUtils = {
+  /**
+   * Read the bytes from a blob, asynchronously.
+   *
+   * @return {Promise}
+   * @resolve {ArrayBuffer} In case of success, the bytes contained in the blob.
+   * @reject {DOMError} In case of error, the underlying DOMError.
+   */
+  readBlob: function readBlob(blob) {
+    let deferred = Promise.defer();
+    let reader = new FileReader();
+    reader.onloadend = function onloadend() {
+      if (reader.readyState != FileReader.DONE) {
+        deferred.reject(reader.error);
+      } else {
+        deferred.resolve(reader.result);
+      }
+    };
+    reader.readAsArrayBuffer(blob);
+    return deferred.promise;
+  }
+};
+
+
+
+
+/**
+ * Singleton providing functionality for capturing web page thumbnails and for
+ * accessing them if already cached.
+ */
+this.PageThumbs = {
+  _initialized: false,
+
+  /**
+   * The calculated width and height of the thumbnails.
+   */
+  _thumbnailWidth : 0,
+  _thumbnailHeight : 0,
+
+  /**
+   * The scheme to use for thumbnail urls.
+   */
+  get scheme() {
+    return "moz-page-thumb";
+  },
+
+  /**
+   * The static host to use for thumbnail urls.
+   */
+  get staticHost() {
+    return "thumbnail";
+  },
+
+  /**
+   * The thumbnails' image type.
+   */
+  get contentType() {
+    return "image/png";
+  },
+
+  init: function PageThumbs_init() {
+    if (!this._initialized) {
+      this._initialized = true;
+      PlacesUtils.history.addObserver(PageThumbsHistoryObserver, true);
+
+      // Migrate the underlying storage, if needed.
+      PageThumbsStorageMigrator.migrate();
+      PageThumbsExpiration.init();
+    }
+  },
+
+  uninit: function PageThumbs_uninit() {
+    if (this._initialized) {
+      this._initialized = false;
+    }
+  },
+
+  /**
+   * Gets the thumbnail image's url for a given web page's url.
+   * @param aUrl The web page's url that is depicted in the thumbnail.
+   * @return The thumbnail image's url.
+   */
+  getThumbnailURL: function PageThumbs_getThumbnailURL(aUrl) {
+    return this.scheme + "://" + this.staticHost +
+           "/?url=" + encodeURIComponent(aUrl) +
+           "&revision=" + PageThumbsStorage.getRevision(aUrl);
+  },
+
+   /**
+    * Gets the path of the thumbnail file for a given web page's
+    * url. This file may or may not exist depending on whether the
+    * thumbnail has been captured or not.
+    *
+    * @param aUrl The web page's url.
+    * @return The path of the thumbnail file.
+    */
+   getThumbnailPath: function PageThumbs_getThumbnailPath(aUrl) {
+     return PageThumbsStorage.getFilePathForURL(aUrl);
+   },
+
+  /**
+   * Asynchronously returns a thumbnail as a blob for the given
+   * window.
+   *
+   * @param aBrowser The <browser> to capture a thumbnail from.
+   * @return {Promise}
+   * @resolve {Blob} The thumbnail, as a Blob.
+   */
+  captureToBlob: function PageThumbs_captureToBlob(aBrowser) {
+    if (!this._prefEnabled()) {
+      return null;
+    }
+
+    let deferred = Promise.defer();
+
+    let canvas = this.createCanvas(aBrowser.contentWindow);
+    this.captureToCanvas(aBrowser, canvas, () => {
+      canvas.toBlob(blob => {
+        deferred.resolve(blob, this.contentType);
+      });
+    });
+
+    return deferred.promise;
+  },
+
+  /**
+   * Captures a thumbnail from a given window and draws it to the given canvas.
+   * Note, when dealing with remote content, this api draws into the passed
+   * canvas asynchronously. Pass aCallback to receive an async callback after
+   * canvas painting has completed.
+   * @param aBrowser The browser to capture a thumbnail from.
+   * @param aCanvas The canvas to draw to. The thumbnail will be scaled to match
+   *   the dimensions of this canvas. If callers pass a 0x0 canvas, the canvas
+   *   will be resized to default thumbnail dimensions just prior to painting.
+   * @param aCallback (optional) A callback invoked once the thumbnail has been
+   *   rendered to aCanvas.
+   * @param aArgs (optional) Additional named parameters:
+   *   fullScale - request that a non-downscaled image be returned.
+   */
+  captureToCanvas: function (aBrowser, aCanvas, aCallback, aArgs) {
+    let telemetryCaptureTime = new Date();
+    let args = {
+      fullScale: aArgs ? aArgs.fullScale : false
+    };
+    this._captureToCanvas(aBrowser, aCanvas, args, (aCanvas) => {
+      Services.telemetry
+              .getHistogramById("FX_THUMBNAILS_CAPTURE_TIME_MS")
+              .add(new Date() - telemetryCaptureTime);
+      if (aCallback) {
+        aCallback(aCanvas);
+      }
+    });
+  },
+
+  /**
+   * Asynchronously check the state of aBrowser to see if it passes a set of
+   * predefined security checks. Consumers should refrain from storing
+   * thumbnails if these checks fail. Note the final result of this call is
+   * transitory as it is based on current navigation state and the type of
+   * content being displayed.
+   *
+   * @param aBrowser The target browser
+   * @param aCallback(aResult) A callback invoked once security checks have
+   *   completed. aResult is a boolean indicating the combined result of the
+   *   security checks performed.
+   */
+  shouldStoreThumbnail: function (aBrowser, aCallback) {
+    // Don't capture in private browsing mode.
+    if (PrivateBrowsingUtils.isBrowserPrivate(aBrowser)) {
+      aCallback(false);
+      return;
+    }
+    if (aBrowser.isRemoteBrowser) {
+      let mm = aBrowser.messageManager;
+      let resultFunc = function (aMsg) {
+        mm.removeMessageListener("Browser:Thumbnail:CheckState:Response", resultFunc);
+        aCallback(aMsg.data.result);
+      }
+      mm.addMessageListener("Browser:Thumbnail:CheckState:Response", resultFunc);
+      try {
+        mm.sendAsyncMessage("Browser:Thumbnail:CheckState");
+      } catch (ex) {
+        Cu.reportError(ex);
+        // If the message manager is not able send our message, taking a content
+        // screenshot is also not going to work: return false.
+        resultFunc({ data: { result: false } });
+      }
+    } else {
+      aCallback(PageThumbUtils.shouldStoreContentThumbnail(aBrowser.contentDocument,
+                                                           aBrowser.docShell));
+    }
+  },
+
+  // The background thumbnail service captures to canvas but doesn't want to
+  // participate in this service's telemetry, which is why this method exists.
+  _captureToCanvas: function (aBrowser, aCanvas, aArgs, aCallback) {
+    if (aBrowser.isRemoteBrowser) {
+      Task.spawn(function* () {
+        let data =
+          yield this._captureRemoteThumbnail(aBrowser, aCanvas.width,
+                                             aCanvas.height, aArgs);
+        let canvas = data.thumbnail;
+        let ctx = canvas.getContext("2d");
+        let imgData = ctx.getImageData(0, 0, canvas.width, canvas.height);
+        aCanvas.width = canvas.width;
+        aCanvas.height = canvas.height;
+        aCanvas.getContext("2d").putImageData(imgData, 0, 0);
+        if (aCallback) {
+          aCallback(aCanvas);
+        }
+      }.bind(this));
+      return;
+    }
+    // The content is a local page, grab a thumbnail sync.
+    PageThumbUtils.createSnapshotThumbnail(aBrowser.contentWindow,
+                                           aCanvas,
+                                           aArgs);
+
+    if (aCallback) {
+      aCallback(aCanvas);
+    }
+  },
+
+  /**
+   * Asynchrnously render an appropriately scaled thumbnail to canvas.
+   *
+   * @param aBrowser The browser to capture a thumbnail from.
+   * @param aWidth The desired canvas width.
+   * @param aHeight The desired canvas height.
+   * @param aArgs (optional) Additional named parameters:
+   *   fullScale - request that a non-downscaled image be returned.
+   * @return a promise
+   */
+  _captureRemoteThumbnail: function (aBrowser, aWidth, aHeight, aArgs) {
+    let deferred = Promise.defer();
+
+    // The index we send with the request so we can identify the
+    // correct response.
+    let index = gRemoteThumbId++;
+
+    // Thumbnail request response handler
+    let mm = aBrowser.messageManager;
+
+    // Browser:Thumbnail:Response handler
+    let thumbFunc = function (aMsg) {
+      // Ignore events unrelated to our request
+      if (aMsg.data.id != index) {
+        return;
+      }
+
+      mm.removeMessageListener("Browser:Thumbnail:Response", thumbFunc);
+      let imageBlob = aMsg.data.thumbnail;
+      let doc = aBrowser.parentElement.ownerDocument;
+      let reader = new FileReader();
+      reader.addEventListener("loadend", function() {
+        let image = doc.createElementNS(PageThumbUtils.HTML_NAMESPACE, "img");
+        image.onload = function () {
+          let thumbnail = doc.createElementNS(PageThumbUtils.HTML_NAMESPACE, "canvas");
+          thumbnail.width = image.naturalWidth;
+          thumbnail.height = image.naturalHeight;
+          let ctx = thumbnail.getContext("2d");
+          ctx.drawImage(image, 0, 0);
+          deferred.resolve({
+            thumbnail: thumbnail
+          });
+        }
+        image.src = reader.result;
+      });
+      // xxx wish there was a way to skip this encoding step
+      reader.readAsDataURL(imageBlob);
+    }
+
+    // Send a thumbnail request
+    mm.addMessageListener("Browser:Thumbnail:Response", thumbFunc);
+    mm.sendAsyncMessage("Browser:Thumbnail:Request", {
+      canvasWidth: aWidth,
+      canvasHeight: aHeight,
+      background: PageThumbUtils.THUMBNAIL_BG_COLOR,
+      id: index,
+      additionalArgs: aArgs
+    });
+
+    return deferred.promise;
+  },
+
+  /**
+   * Captures a thumbnail for the given browser and stores it to the cache.
+   * @param aBrowser The browser to capture a thumbnail for.
+   * @param aCallback The function to be called when finished (optional).
+   */
+  captureAndStore: function PageThumbs_captureAndStore(aBrowser, aCallback) {
+    if (!this._prefEnabled()) {
+      return;
+    }
+
+    let url = aBrowser.currentURI.spec;
+    let originalURL;
+    let channelError = false;
+
+    Task.spawn((function* task() {
+      if (!aBrowser.isRemoteBrowser) {
+        let channel = aBrowser.docShell.currentDocumentChannel;
+        originalURL = channel.originalURI.spec;
+        // see if this was an error response.
+        channelError = PageThumbUtils.isChannelErrorResponse(channel);
+      } else {
+        let resp = yield new Promise(resolve => {
+          let mm = aBrowser.messageManager;
+          let respName = "Browser:Thumbnail:GetOriginalURL:Response";
+          mm.addMessageListener(respName, function onResp(msg) {
+            mm.removeMessageListener(respName, onResp);
+            resolve(msg.data);
+          });
+          mm.sendAsyncMessage("Browser:Thumbnail:GetOriginalURL");
+        });
+        originalURL = resp.originalURL || url;
+        channelError = resp.channelError;
+      }
+
+      let isSuccess = true;
+      try {
+        let blob = yield this.captureToBlob(aBrowser);
+        let buffer = yield TaskUtils.readBlob(blob);
+        yield this._store(originalURL, url, buffer, channelError);
+      } catch (ex) {
+        Components.utils.reportError("Exception thrown during thumbnail capture: '" + ex + "'");
+        isSuccess = false;
+      }
+      if (aCallback) {
+        aCallback(isSuccess);
+      }
+    }).bind(this));
+  },
+
+  /**
+   * Checks if an existing thumbnail for the specified URL is either missing
+   * or stale, and if so, captures and stores it.  Once the thumbnail is stored,
+   * an observer service notification will be sent, so consumers should observe
+   * such notifications if they want to be notified of an updated thumbnail.
+   *
+   * @param aBrowser The content window of this browser will be captured.
+   * @param aCallback The function to be called when finished (optional).
+   */
+  captureAndStoreIfStale: function PageThumbs_captureAndStoreIfStale(aBrowser, aCallback) {
+    let url = aBrowser.currentURI.spec;
+    PageThumbsStorage.isFileRecentForURL(url).then(recent => {
+      if (!recent &&
+          // Careful, the call to PageThumbsStorage is async, so the browser may
+          // have navigated away from the URL or even closed.
+          aBrowser.currentURI &&
+          aBrowser.currentURI.spec == url) {
+        this.captureAndStore(aBrowser, aCallback);
+      } else if (aCallback) {
+        aCallback(true);
+      }
+    }, err => {
+      if (aCallback)
+        aCallback(false);
+    });
+  },
+
+  /**
+   * Stores data to disk for the given URLs.
+   *
+   * NB: The background thumbnail service calls this, too.
+   *
+   * @param aOriginalURL The URL with which the capture was initiated.
+   * @param aFinalURL The URL to which aOriginalURL ultimately resolved.
+   * @param aData An ArrayBuffer containing the image data.
+   * @param aNoOverwrite If true and files for the URLs already exist, the files
+   *                     will not be overwritten.
+   * @return {Promise}
+   */
+  _store: function PageThumbs__store(aOriginalURL, aFinalURL, aData, aNoOverwrite) {
+    return Task.spawn(function* () {
+      let telemetryStoreTime = new Date();
+      yield PageThumbsStorage.writeData(aFinalURL, aData, aNoOverwrite);
+      Services.telemetry.getHistogramById("FX_THUMBNAILS_STORE_TIME_MS")
+        .add(new Date() - telemetryStoreTime);
+
+      Services.obs.notifyObservers(null, "page-thumbnail:create", aFinalURL);
+      // We've been redirected. Create a copy of the current thumbnail for
+      // the redirect source. We need to do this because:
+      //
+      // 1) Users can drag any kind of links onto the newtab page. If those
+      //    links redirect to a different URL then we want to be able to
+      //    provide thumbnails for both of them.
+      //
+      // 2) The newtab page should actually display redirect targets, only.
+      //    Because of bug 559175 this information can get lost when using
+      //    Sync and therefore also redirect sources appear on the newtab
+      //    page. We also want thumbnails for those.
+      if (aFinalURL != aOriginalURL) {
+        yield PageThumbsStorage.copy(aFinalURL, aOriginalURL, aNoOverwrite);
+        Services.obs.notifyObservers(null, "page-thumbnail:create", aOriginalURL);
+      }
+    });
+  },
+
+  /**
+   * Register an expiration filter.
+   *
+   * When thumbnails are going to expire, each registered filter is asked for a
+   * list of thumbnails to keep.
+   *
+   * The filter (if it is a callable) or its filterForThumbnailExpiration method
+   * (if the filter is an object) is called with a single argument.  The
+   * argument is a callback function.  The filter must call the callback
+   * function and pass it an array of zero or more URLs.  (It may do so
+   * asynchronously.)  Thumbnails for those URLs will be except from expiration.
+   *
+   * @param aFilter callable, or object with filterForThumbnailExpiration method
+   */
+  addExpirationFilter: function PageThumbs_addExpirationFilter(aFilter) {
+    PageThumbsExpiration.addFilter(aFilter);
+  },
+
+  /**
+   * Unregister an expiration filter.
+   * @param aFilter A filter that was previously passed to addExpirationFilter.
+   */
+  removeExpirationFilter: function PageThumbs_removeExpirationFilter(aFilter) {
+    PageThumbsExpiration.removeFilter(aFilter);
+  },
+
+  /**
+   * Creates a new hidden canvas element.
+   * @param aWindow The document of this window will be used to create the
+   *                canvas.  If not given, the hidden window will be used.
+   * @return The newly created canvas.
+   */
+  createCanvas: function PageThumbs_createCanvas(aWindow) {
+    return PageThumbUtils.createCanvas(aWindow);
+  },
+
+  _prefEnabled: function PageThumbs_prefEnabled() {
+    try {
+      return !Services.prefs.getBoolPref("browser.pagethumbnails.capturing_disabled");
+    }
+    catch (e) {
+      return true;
+    }
+  },
+};
+
+this.PageThumbsStorage = {
+  // The path for the storage
+  _path: null,
+  get path() {
+    if (!this._path) {
+      this._path = OS.Path.join(OS.Constants.Path.localProfileDir, THUMBNAIL_DIRECTORY);
+    }
+    return this._path;
+  },
+
+  ensurePath: function Storage_ensurePath() {
+    // Create the directory (ignore any error if the directory
+    // already exists). As all writes are done from the PageThumbsWorker
+    // thread, which serializes its operations, this ensures that
+    // future operations can proceed without having to check whether
+    // the directory exists.
+    return PageThumbsWorker.post("makeDir",
+      [this.path, {ignoreExisting: true}]).then(
+        null,
+        function onError(aReason) {
+          Components.utils.reportError("Could not create thumbnails directory" + aReason);
+        });
+  },
+
+  getLeafNameForURL: function Storage_getLeafNameForURL(aURL) {
+    if (typeof aURL != "string") {
+      throw new TypeError("Expecting a string");
+    }
+    let hash = this._calculateMD5Hash(aURL);
+    return hash + ".png";
+  },
+
+  getFilePathForURL: function Storage_getFilePathForURL(aURL) {
+    return OS.Path.join(this.path, this.getLeafNameForURL(aURL));
+  },
+
+  _revisionTable: {},
+
+  // Generate an arbitrary revision tag, i.e. one that can't be used to
+  // infer URL frecency.
+  _updateRevision(aURL) {
+    // Initialize with a random value and increment on each update. Wrap around
+    // modulo _revisionRange, so that even small values carry no meaning.
+    let rev = this._revisionTable[aURL];
+    if (rev == null)
+      rev = Math.floor(Math.random() * this._revisionRange);
+    this._revisionTable[aURL] = (rev + 1) % this._revisionRange;
+  },
+
+  // If two thumbnails with the same URL and revision are in cache at the
+  // same time, the image loader may pick the stale thumbnail in some cases.
+  // Therefore _revisionRange must be large enough to prevent this, e.g.
+  // in the pathological case image.cache.size (5MB by default) could fill
+  // with (abnormally small) 10KB thumbnail images if the browser session
+  // runs long enough (though this is unlikely as thumbnails are usually
+  // only updated every MAX_THUMBNAIL_AGE_SECS).
+  _revisionRange: 8192,
+
+  /**
+  * Return a revision tag for the thumbnail stored for a given URL.
+  *
+  * @param aURL The URL spec string
+  * @return A revision tag for the corresponding thumbnail. Returns a changed
+  * value whenever the stored thumbnail changes.
+  */
+  getRevision(aURL) {
+    let rev = this._revisionTable[aURL];
+    if (rev == null) {
+      this._updateRevision(aURL);
+      rev = this._revisionTable[aURL];
+    }
+    return rev;
+  },
+
+  /**
+   * Write the contents of a thumbnail, off the main thread.
+   *
+   * @param {string} aURL The url for which to store a thumbnail.
+   * @param {ArrayBuffer} aData The data to store in the thumbnail, as
+   * an ArrayBuffer. This array buffer will be detached and cannot be
+   * reused after the copy.
+   * @param {boolean} aNoOverwrite If true and the thumbnail's file already
+   * exists, the file will not be overwritten.
+   *
+   * @return {Promise}
+   */
+  writeData: function Storage_writeData(aURL, aData, aNoOverwrite) {
+    let path = this.getFilePathForURL(aURL);
+    this.ensurePath();
+    aData = new Uint8Array(aData);
+    let msg = [
+      path,
+      aData,
+      {
+        tmpPath: path + ".tmp",
+        bytes: aData.byteLength,
+        noOverwrite: aNoOverwrite,
+        flush: false /* thumbnails do not require the level of guarantee provided by flush*/
+      }];
+    return PageThumbsWorker.post("writeAtomic", msg,
+      msg /* we don't want that message garbage-collected,
+           as OS.Shared.Type.void_t.in_ptr.toMsg uses C-level
+           memory tricks to enforce zero-copy*/).
+      then(() => this._updateRevision(aURL), this._eatNoOverwriteError(aNoOverwrite));
+  },
+
+  /**
+   * Copy a thumbnail, off the main thread.
+   *
+   * @param {string} aSourceURL The url of the thumbnail to copy.
+   * @param {string} aTargetURL The url of the target thumbnail.
+   * @param {boolean} aNoOverwrite If true and the target file already exists,
+   * the file will not be overwritten.
+   *
+   * @return {Promise}
+   */
+  copy: function Storage_copy(aSourceURL, aTargetURL, aNoOverwrite) {
+    this.ensurePath();
+    let sourceFile = this.getFilePathForURL(aSourceURL);
+    let targetFile = this.getFilePathForURL(aTargetURL);
+    let options = { noOverwrite: aNoOverwrite };
+    return PageThumbsWorker.post("copy", [sourceFile, targetFile, options]).
+      then(() => this._updateRevision(aTargetURL), this._eatNoOverwriteError(aNoOverwrite));
+  },
+
+  /**
+   * Remove a single thumbnail, off the main thread.
+   *
+   * @return {Promise}
+   */
+  remove: function Storage_remove(aURL) {
+    return PageThumbsWorker.post("remove", [this.getFilePathForURL(aURL)]);
+  },
+
+  /**
+   * Remove all thumbnails, off the main thread.
+   *
+   * @return {Promise}
+   */
+  wipe: Task.async(function* Storage_wipe() {
+    //
+    // This operation may be launched during shutdown, so we need to
+    // take a few precautions to ensure that:
+    //
+    // 1. it is not interrupted by shutdown, in which case we
+    //    could be leaving privacy-sensitive files on disk;
+    // 2. it is not launched too late during shutdown, in which
+    //    case this could cause shutdown freezes (see bug 1005487,
+    //    which will eventually be fixed by bug 965309)
+    //
+
+    let blocker = () => promise;
+
+    // The following operation will rise an error if we have already
+    // reached profileBeforeChange, in which case it is too late
+    // to clear the thumbnail wipe.
+    AsyncShutdown.profileBeforeChange.addBlocker(
+      "PageThumbs: removing all thumbnails",
+      blocker);
+
+    // Start the work only now that `profileBeforeChange` has had
+    // a chance to throw an error.
+
+    let promise = PageThumbsWorker.post("wipe", [this.path]);
+    try {
+      yield promise;
+    }  finally {
+       // Generally, we will be done much before profileBeforeChange,
+       // so let's not hoard blockers.
+       if ("removeBlocker" in AsyncShutdown.profileBeforeChange) {
+         // `removeBlocker` was added with bug 985655. In the interest
+         // of backporting, let's degrade gracefully if `removeBlocker`
+         // doesn't exist.
+         AsyncShutdown.profileBeforeChange.removeBlocker(blocker);
+       }
+    }
+  }),
+
+  fileExistsForURL: function Storage_fileExistsForURL(aURL) {
+    return PageThumbsWorker.post("exists", [this.getFilePathForURL(aURL)]);
+  },
+
+  isFileRecentForURL: function Storage_isFileRecentForURL(aURL) {
+    return PageThumbsWorker.post("isFileRecent",
+                                 [this.getFilePathForURL(aURL),
+                                  MAX_THUMBNAIL_AGE_SECS]);
+  },
+
+  _calculateMD5Hash: function Storage_calculateMD5Hash(aValue) {
+    let hash = gCryptoHash;
+    let value = gUnicodeConverter.convertToByteArray(aValue);
+
+    hash.init(hash.MD5);
+    hash.update(value, value.length);
+    return this._convertToHexString(hash.finish(false));
+  },
+
+  _convertToHexString: function Storage_convertToHexString(aData) {
+    let hex = "";
+    for (let i = 0; i < aData.length; i++)
+      hex += ("0" + aData.charCodeAt(i).toString(16)).slice(-2);
+    return hex;
+  },
+
+  /**
+   * For functions that take a noOverwrite option, OS.File throws an error if
+   * the target file exists and noOverwrite is true.  We don't consider that an
+   * error, and we don't want such errors propagated.
+   *
+   * @param {aNoOverwrite} The noOverwrite option used in the OS.File operation.
+   *
+   * @return {function} A function that should be passed as the second argument
+   * to then() (the `onError` argument).
+   */
+  _eatNoOverwriteError: function Storage__eatNoOverwriteError(aNoOverwrite) {
+    return function onError(err) {
+      if (!aNoOverwrite ||
+          !(err instanceof OS.File.Error) ||
+          !err.becauseExists) {
+        throw err;
+      }
+    };
+  },
+
+  // Deprecated, please do not use
+  getFileForURL: function Storage_getFileForURL_DEPRECATED(aURL) {
+    Deprecated.warning("PageThumbs.getFileForURL is deprecated. Please use PageThumbs.getFilePathForURL and OS.File",
+                       "https://developer.mozilla.org/docs/JavaScript_OS.File");
+    // Note: Once this method has been removed, we can get rid of the dependency towards FileUtils
+    return new FileUtils.File(PageThumbsStorage.getFilePathForURL(aURL));
+  }
+};
+
+var PageThumbsStorageMigrator = {
+  get currentVersion() {
+    try {
+      return Services.prefs.getIntPref(PREF_STORAGE_VERSION);
+    } catch (e) {
+      // The pref doesn't exist, yet. Return version 0.
+      return 0;
+    }
+  },
+
+  set currentVersion(aVersion) {
+    Services.prefs.setIntPref(PREF_STORAGE_VERSION, aVersion);
+  },
+
+  migrate: function Migrator_migrate() {
+    let version = this.currentVersion;
+
+    // Storage version 1 never made it to beta.
+    // At the time of writing only Windows had (ProfD != ProfLD) and we
+    // needed to move thumbnails from the roaming profile to the locale
+    // one so that they're not needlessly included in backups and/or
+    // written via SMB.
+
+    // Storage version 2 also never made it to beta.
+    // The thumbnail folder structure has been changed and old thumbnails
+    // were not migrated. Instead, we just renamed the current folder to
+    // "<name>-old" and will remove it later.
+
+    if (version < 3) {
+      this.migrateToVersion3();
+    }
+
+    this.currentVersion = LATEST_STORAGE_VERSION;
+  },
+
+  /**
+   * Bug 239254 added support for having the disk cache and thumbnail
+   * directories on a local path (i.e. ~/.cache/) under Linux. We'll first
+   * try to move the old thumbnails to their new location. If that's not
+   * possible (because ProfD might be on a different file system than
+   * ProfLD) we'll just discard them.
+   *
+   * @param {string*} local The path to the local profile directory.
+   * Used for testing. Default argument is good for all non-testing uses.
+   * @param {string*} roaming The path to the roaming profile directory.
+   * Used for testing. Default argument is good for all non-testing uses.
+   */
+  migrateToVersion3: function Migrator_migrateToVersion3(
+    local = OS.Constants.Path.localProfileDir,
+    roaming = OS.Constants.Path.profileDir) {
+    PageThumbsWorker.post(
+      "moveOrDeleteAllThumbnails",
+      [OS.Path.join(roaming, THUMBNAIL_DIRECTORY),
+       OS.Path.join(local, THUMBNAIL_DIRECTORY)]
+    );
+  }
+};
+
+var PageThumbsExpiration = {
+  _filters: [],
+
+  init: function Expiration_init() {
+    gUpdateTimerManager.registerTimer("browser-cleanup-thumbnails", this,
+                                      EXPIRATION_INTERVAL_SECS);
+  },
+
+  addFilter: function Expiration_addFilter(aFilter) {
+    this._filters.push(aFilter);
+  },
+
+  removeFilter: function Expiration_removeFilter(aFilter) {
+    let index = this._filters.indexOf(aFilter);
+    if (index > -1)
+      this._filters.splice(index, 1);
+  },
+
+  notify: function Expiration_notify(aTimer) {
+    let urls = [];
+    let filtersToWaitFor = this._filters.length;
+
+    let expire = function expire() {
+      this.expireThumbnails(urls);
+    }.bind(this);
+
+    // No registered filters.
+    if (!filtersToWaitFor) {
+      expire();
+      return;
+    }
+
+    function filterCallback(aURLs) {
+      urls = urls.concat(aURLs);
+      if (--filtersToWaitFor == 0)
+        expire();
+    }
+
+    for (let filter of this._filters) {
+      if (typeof filter == "function")
+        filter(filterCallback)
+      else
+        filter.filterForThumbnailExpiration(filterCallback);
+    }
+  },
+
+  expireThumbnails: function Expiration_expireThumbnails(aURLsToKeep) {
+    let keep = aURLsToKeep.map(url => PageThumbsStorage.getLeafNameForURL(url));
+    let msg = [
+      PageThumbsStorage.path,
+      keep,
+      EXPIRATION_MIN_CHUNK_SIZE
+    ];
+
+    return PageThumbsWorker.post(
+      "expireFilesInDirectory",
+      msg
+    );
+  }
+};
+
+/**
+ * Interface to a dedicated thread handling I/O
+ */
+var PageThumbsWorker = new BasePromiseWorker("resource://gre/modules/PageThumbsWorker.js");
+// As the PageThumbsWorker performs I/O, we can receive instances of
+// OS.File.Error, so we need to install a decoder.
+PageThumbsWorker.ExceptionHandlers["OS.File.Error"] = OS.File.Error.fromMsg;
+
+var PageThumbsHistoryObserver = {
+  onDeleteURI(aURI, aGUID) {
+    PageThumbsStorage.remove(aURI.spec);
+  },
+
+  onClearHistory() {
+    PageThumbsStorage.wipe();
+  },
+
+  onTitleChanged: function () {},
+  onBeginUpdateBatch: function () {},
+  onEndUpdateBatch: function () {},
+  onVisit: function () {},
+  onPageChanged: function () {},
+  onDeleteVisits: function () {},
+
+  QueryInterface: XPCOMUtils.generateQI([Ci.nsINavHistoryObserver,
+                                         Ci.nsISupportsWeakReference])
+};