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+<!-- 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/. -->
+<!DOCTYPE HTML>
+<html>
+<!--
+Test that we only render visible tree items.
+-->
+<head>
+  <meta charset="utf-8">
+  <title>Tree component test</title>
+  <script type="application/javascript" src="chrome://mochikit/content/tests/SimpleTest/SimpleTest.js"></script>
+  <link rel="stylesheet" type="text/css" href="chrome://mochikit/content/tests/SimpleTest/test.css">
+</head>
+<body>
+<pre id="test">
+<script src="head.js" type="application/javascript;version=1.8"></script>
+<script type="application/javascript;version=1.8">
+window.onload = Task.async(function* () {
+  try {
+    function getSpacerHeights() {
+      return {
+        top: document.querySelector(".tree > div:first-of-type").clientHeight,
+        bottom: document.querySelector(".tree > div:last-of-type").clientHeight,
+      };
+    }
+
+    const ITEM_HEIGHT = 3;
+
+    const ReactDOM = browserRequire("devtools/client/shared/vendor/react-dom");
+    const React = browserRequire("devtools/client/shared/vendor/react");
+    const Tree = React.createFactory(browserRequire("devtools/client/shared/components/tree"));
+
+    const tree = ReactDOM.render(
+      Tree(Object.assign({}, TEST_TREE_INTERFACE, { itemHeight: ITEM_HEIGHT })),
+      window.document.body);
+
+    TEST_TREE.expanded = new Set("ABCDEFGHIJKLMNO".split(""));
+
+    yield setState(tree, {
+      height: 3 * ITEM_HEIGHT,
+      scroll: 1 * ITEM_HEIGHT
+    });
+
+    isRenderedTree(document.body.textContent, [
+      "A:false",
+      "-B:false",
+      "--E:false",
+      "---K:false",
+      "---L:false",
+    ], "Tree should show the 2nd, 3rd, and 4th items + buffer of 1 item at each end");
+
+    let spacers = getSpacerHeights();
+    is(spacers.top, 0, "Top spacer has the correct height");
+    is(spacers.bottom, 10 * ITEM_HEIGHT, "Bottom spacer has the correct height");
+
+    yield setState(tree, {
+      height: 2 * ITEM_HEIGHT,
+      scroll: 3 * ITEM_HEIGHT
+    });
+
+    isRenderedTree(document.body.textContent, [
+      "--E:false",
+      "---K:false",
+      "---L:false",
+      "--F:false",
+    ], "Tree should show the 4th and 5th item + buffer of 1 item at each end");
+
+    spacers = getSpacerHeights();
+    is(spacers.top, 2 * ITEM_HEIGHT, "Top spacer has the correct height");
+    is(spacers.bottom, 9 * ITEM_HEIGHT, "Bottom spacer has the correct height");
+
+    // Set height to 2 items + 1 pixel at each end, scroll so that 4 items are visible
+    // (2 fully, 2 partially with 1 visible pixel)
+    yield setState(tree, {
+      height: 2 * ITEM_HEIGHT + 2,
+      scroll: 3 * ITEM_HEIGHT - 1
+    });
+
+    isRenderedTree(document.body.textContent, [
+      "-B:false",
+      "--E:false",
+      "---K:false",
+      "---L:false",
+      "--F:false",
+      "--G:false",
+    ], "Tree should show the 4 visible items + buffer of 1 item at each end");
+
+    spacers = getSpacerHeights();
+    is(spacers.top, 1 * ITEM_HEIGHT, "Top spacer has the correct height");
+    is(spacers.bottom, 8 * ITEM_HEIGHT, "Bottom spacer has the correct height");
+
+    yield setState(tree, {
+      height: 20 * ITEM_HEIGHT,
+      scroll: 0
+    });
+
+    isRenderedTree(document.body.textContent, [
+      "A:false",
+      "-B:false",
+      "--E:false",
+      "---K:false",
+      "---L:false",
+      "--F:false",
+      "--G:false",
+      "-C:false",
+      "--H:false",
+      "--I:false",
+      "-D:false",
+      "--J:false",
+      "M:false",
+      "-N:false",
+      "--O:false",
+    ], "Tree should show all rows");
+
+    spacers = getSpacerHeights();
+    is(spacers.top, 0, "Top spacer has zero height");
+    is(spacers.bottom, 0, "Bottom spacer has zero height");
+  } catch(e) {
+    ok(false, "Got an error: " + DevToolsUtils.safeErrorString(e));
+  } finally {
+    SimpleTest.finish();
+  }
+});
+</script>
+</pre>
+</body>
+</html>