1 files changed, 118 insertions, 0 deletions
diff --git a/browser/base/content/test/performance/browser_tabdetach.js b/browser/base/content/test/performance/browser_tabdetach.js
new file mode 100644
index 0000000000..a860362f1f
--- /dev/null
+++ b/browser/base/content/test/performance/browser_tabdetach.js
@@ -0,0 +1,118 @@
+"use strict";
+
+/**
+ * WHOA THERE: We should never be adding new things to EXPECTED_REFLOWS. This
+ * list should slowly go away as we improve the performance of the front-end.
+ * Instead of adding more reflows to the list, you should be modifying your code
+ * to avoid the reflow.
+ *
+ * See https://firefox-source-docs.mozilla.org/performance/bestpractices.html
+ * for tips on how to do that.
+ */
+const EXPECTED_REFLOWS = [
+  {
+    stack: [
+      "clientX@chrome://browser/content/tabbrowser-tabs.js",
+      "startTabDrag@chrome://browser/content/tabbrowser-tabs.js",
+      "on_dragstart@chrome://browser/content/tabbrowser-tabs.js",
+      "handleEvent@chrome://browser/content/tabbrowser-tabs.js",
+      "synthesizeMouseAtPoint@chrome://mochikit/content/tests/SimpleTest/EventUtils.js",
+      "synthesizeMouse@chrome://mochikit/content/tests/SimpleTest/EventUtils.js",
+      "synthesizePlainDragAndDrop@chrome://mochikit/content/tests/SimpleTest/EventUtils.js",
+    ],
+    maxCount: 2,
+  },
+
+  {
+    stack: [
+      "startTabDrag@chrome://browser/content/tabbrowser-tabs.js",
+      "on_dragstart@chrome://browser/content/tabbrowser-tabs.js",
+      "handleEvent@chrome://browser/content/tabbrowser-tabs.js",
+      "synthesizeMouseAtPoint@chrome://mochikit/content/tests/SimpleTest/EventUtils.js",
+      "synthesizeMouse@chrome://mochikit/content/tests/SimpleTest/EventUtils.js",
+      "synthesizePlainDragAndDrop@chrome://mochikit/content/tests/SimpleTest/EventUtils.js",
+    ],
+  },
+];
+
+/**
+ * This test ensures that there are no unexpected uninterruptible reflows when
+ * detaching a tab via drag and drop. The first testcase tests a non-overflowed
+ * tab strip, and the second tests an overflowed one.
+ */
+
+add_task(async function test_detach_not_overflowed() {
+  await ensureNoPreloadedBrowser();
+  await createTabs(1);
+
+  // Make sure we didn't overflow, as expected
+  await TestUtils.waitForCondition(() => {
+    return !gBrowser.tabContainer.hasAttribute("overflow");
+  });
+
+  let win;
+  await withPerfObserver(
+    async function () {
+      win = await detachTab(gBrowser.tabs[1]);
+    },
+    {
+      expectedReflows: EXPECTED_REFLOWS,
+      // we are opening a whole new window, so there's no point in tracking
+      // rects being painted
+      frames: { filter: rects => [] },
+    }
+  );
+
+  await BrowserTestUtils.closeWindow(win);
+  win = null;
+});
+
+add_task(async function test_detach_overflowed() {
+  const TAB_COUNT_FOR_OVERFLOW = computeMaxTabCount();
+  await createTabs(TAB_COUNT_FOR_OVERFLOW + 1);
+
+  // Make sure we overflowed, as expected
+  await TestUtils.waitForCondition(() => {
+    return gBrowser.tabContainer.hasAttribute("overflow");
+  });
+
+  let win;
+  await withPerfObserver(
+    async function () {
+      win = await detachTab(
+        gBrowser.tabs[Math.floor(TAB_COUNT_FOR_OVERFLOW / 2)]
+      );
+    },
+    {
+      expectedReflows: EXPECTED_REFLOWS,
+      // we are opening a whole new window, so there's no point in tracking
+      // rects being painted
+      frames: { filter: rects => [] },
+    }
+  );
+
+  await BrowserTestUtils.closeWindow(win);
+  win = null;
+
+  await removeAllButFirstTab();
+});
+
+async function detachTab(tab) {
+  let newWindowPromise = BrowserTestUtils.waitForNewWindow();
+
+  await EventUtils.synthesizePlainDragAndDrop({
+    srcElement: tab,
+
+    // destElement is null because tab detaching happens due
+    // to a drag'n'drop on an invalid drop target.
+    destElement: null,
+
+    // don't move horizontally because that could cause a tab move
+    // animation, and there's code to prevent a tab detaching if
+    // the dragged tab is released while the animation is running.
+    stepX: 0,
+    stepY: 100,
+  });
+
+  return newWindowPromise;
+}