diff -r 000000000000 -r 6474c204b198 browser/devtools/shared/test/browser_layoutHelpers.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/devtools/shared/test/browser_layoutHelpers.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,101 @@
+/* Any copyright is dedicated to the Public Domain.
+ * http://creativecommons.org/publicdomain/zero/1.0/ */
+
+// Tests that scrollIntoViewIfNeeded works properly.
+
+let imported = {};
+Components.utils.import("resource://gre/modules/devtools/LayoutHelpers.jsm",
+    imported);
+registerCleanupFunction(function () {
+  imported = {};
+});
+
+let LayoutHelpers = imported.LayoutHelpers;
+
+const TEST_URI = "http://example.com/browser/browser/devtools/shared/test/browser_layoutHelpers.html";
+
+function test() {
+  addTab(TEST_URI, function(browser, tab) {
+    info("Starting browser_layoutHelpers.js");
+    let doc = browser.contentDocument;
+    runTest(doc.defaultView, doc.getElementById('some'));
+    gBrowser.removeCurrentTab();
+    finish();
+  });
+}
+
+function runTest(win, some) {
+  let lh = new LayoutHelpers(win);
+
+  some.style.top = win.innerHeight + 'px';
+  some.style.left = win.innerWidth + 'px';
+  // The tests start with a black 2x2 pixels square below bottom right.
+  // Do not resize the window during the tests.
+
+  win.scroll(win.innerWidth / 2, win.innerHeight + 2);  // Above the viewport.
+  lh.scrollIntoViewIfNeeded(some);
+  is(win.scrollY, Math.floor(win.innerHeight / 2) + 1,
+     'Element completely hidden above should appear centered.');
+
+  win.scroll(win.innerWidth / 2, win.innerHeight + 1);  // On the top edge.
+  lh.scrollIntoViewIfNeeded(some);
+  is(win.scrollY, win.innerHeight,
+     'Element partially visible above should appear above.');
+
+  win.scroll(win.innerWidth / 2, 0);  // Just below the viewport.
+  lh.scrollIntoViewIfNeeded(some);
+  is(win.scrollY, Math.floor(win.innerHeight / 2) + 1,
+     'Element completely hidden below should appear centered.');
+
+  win.scroll(win.innerWidth / 2, 1);  // On the bottom edge.
+  lh.scrollIntoViewIfNeeded(some);
+  is(win.scrollY, 2,
+     'Element partially visible below should appear below.');
+
+
+  win.scroll(win.innerWidth / 2, win.innerHeight + 2);  // Above the viewport.
+  lh.scrollIntoViewIfNeeded(some, false);
+  is(win.scrollY, win.innerHeight,
+     'Element completely hidden above should appear above ' +
+     'if parameter is false.');
+
+  win.scroll(win.innerWidth / 2, win.innerHeight + 1);  // On the top edge.
+  lh.scrollIntoViewIfNeeded(some, false);
+  is(win.scrollY, win.innerHeight,
+     'Element partially visible above should appear above ' +
+     'if parameter is false.');
+
+  win.scroll(win.innerWidth / 2, 0);  // Below the viewport.
+  lh.scrollIntoViewIfNeeded(some, false);
+  is(win.scrollY, 2,
+     'Element completely hidden below should appear below ' +
+     'if parameter is false.');
+
+  win.scroll(win.innerWidth / 2, 1);  // On the bottom edge.
+  lh.scrollIntoViewIfNeeded(some, false);
+  is(win.scrollY, 2,
+     'Element partially visible below should appear below ' +
+     'if parameter is false.');
+
+  // The case of iframes.
+  win.scroll(0, 0);
+
+  let frame = win.document.getElementById('frame');
+  let fwin = frame.contentWindow;
+
+  frame.style.top = win.innerHeight + 'px';
+  frame.style.left = win.innerWidth + 'px';
+
+  fwin.addEventListener('load', function frameLoad() {
+    let some = fwin.document.getElementById('some');
+    lh.scrollIntoViewIfNeeded(some);
+    is(win.scrollX, Math.floor(win.innerWidth / 2) + 20,
+       'Scrolling from an iframe should center the iframe vertically.');
+    is(win.scrollY, Math.floor(win.innerHeight / 2) + 20,
+       'Scrolling from an iframe should center the iframe horizontally.');
+    is(fwin.scrollX, Math.floor(fwin.innerWidth / 2) + 1,
+       'Scrolling from an iframe should center the element vertically.');
+    is(fwin.scrollY, Math.floor(fwin.innerHeight / 2) + 1,
+       'Scrolling from an iframe should center the element horizontally.');
+  }, false);
+}