Similar to bug 1363505, but blocked until we can make the tab strip cause reflows more deterministically (instead of via rAF). Specific cases to be tested: * Tab opening (tab strip switches to overflow) * Tab opening (in overflow state) * Tab closing (in overflow state) * Tab closing (tab strip underflows) * Tab switching (selected tab is scrolled out of view)

Finally coming back around to this. What we've already got: * Tab opening (tab strip switches to overflow) * Tab closing (tab strip underflows) What we still need: * Tab opening (in overflow state) * Tab closing (in overflow state) * Tab switching (selected tab is scrolled out of view)

Comment on attachment 8930620 [details] Bug 1367797 - Add reflow tests for adding, removing and switching tabs while the tab strip is overflowed. https://reviewboard.mozilla.org/r/201380/#review210210 Looks good, thanks. I wonder if there would be any point in testing tab closing without animation. Also, would it be useful to test closing several tabs at once? ie. should we put a reflow observer around the removeAllButFirstTab call? And if so should we do it both in an overflow and a non-overflow case? Should we check that no reflow happens when closing a window? (a window with one tab / a window with multiple tabs) (just giving food for thoughts here, none of these new cases is required for landing) ::: browser/base/content/test/performance/browser_tabstrip_overflow_underflow_reflows.js:57 (Diff revision 1) > > - await withReflowObserver(async function() { > + Assert.ok(gBrowser.tabContainer.hasAttribute("overflow"), > + "Tabs should now be overflowed."); > + > + // Now test that opening and closing a tab while overflowed doesn't cause > + // us to overflow. s/overflow/reflow/ ::: browser/base/content/test/performance/browser_tabstrip_overflow_underflow_reflows.js:88 (Diff revision 1) > + "First tab should be scrolled out of view."); > + > + // Now switch to the first tab. We shouldn't flush layout at all. > + await withReflowObserver(async function(dirtyFrame) { > + let switchDone = BrowserTestUtils.waitForEvent(window, "TabSwitchDone"); > + await BrowserTestUtils.switchTab(gBrowser, firstTab); BrowserTestUtils.switchTab returns a promise that waits for the TabSwitchDone event already.

Pushed by mconley@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/cfa04fd0f319 Add reflow tests for adding, removing and switching tabs while the tab strip is overflowed. r=florian

Comment on attachment 8930620 [details] Bug 1367797 - Add reflow tests for adding, removing and switching tabs while the tab strip is overflowed. https://reviewboard.mozilla.org/r/201380/#review210210 Good ideas! I've filed bug 1424377 for them.

Backed out changeset cfa04fd0f319 (bug 1367797) for causing browser-chrome failures on browser_tabstrip_overflow_underflow_reflows.js r=backout on a CLOSED TREE https://treeherder.mozilla.org/logviewer.html#?job_id=150914547&repo=autoland https://hg.mozilla.org/integration/autoland/rev/7d3a7c5c694253c8d0382f368067b2c26a6ec192 https://treeherder.mozilla.org/#/jobs?repo=autoland&revision=cfa04fd0f3198bdefc3dbd3293756e0f1e101b96

Made some minor adjustments to make the test more resilient across different display sizes.

Pushed by mconley@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/c1389acf296a Add reflow tests for adding, removing and switching tabs while the tab strip is overflowed. r=florian