1 files changed, 65 insertions, 0 deletions
diff --git a/browser/base/content/test/performance/browser_toolbariconcolor_restyles.js b/browser/base/content/test/performance/browser_toolbariconcolor_restyles.js
new file mode 100644
index 0000000000..890c8f3c80
--- /dev/null
+++ b/browser/base/content/test/performance/browser_toolbariconcolor_restyles.js
@@ -0,0 +1,65 @@
+"use strict";
+
+/**
+ * Ensure redundant style flushes are not triggered when switching between windows
+ */
+add_task(async function test_toolbar_element_restyles_on_activation() {
+  let restyles = {
+    win1: {},
+    win2: {},
+  };
+
+  // create a window and snapshot the elementsStyled
+  let win1 = await BrowserTestUtils.openNewBrowserWindow();
+  await new Promise(resolve => waitForFocus(resolve, win1));
+
+  // create a 2nd window and snapshot the elementsStyled
+  let win2 = await BrowserTestUtils.openNewBrowserWindow();
+  await new Promise(resolve => waitForFocus(resolve, win2));
+
+  // (De)-activate both windows once before we take a measurement. The first
+  // (de-)activation may flush styles, after that the style data should be
+  // cached.
+  win1.focus();
+  win2.focus();
+
+  // Flush any pending styles before we take a measurement.
+  win1.getComputedStyle(win1.document.firstElementChild);
+  win2.getComputedStyle(win2.document.firstElementChild);
+
+  // Clear the focused element from each window so that when
+  // we raise them, the focus of the element doesn't cause an
+  // unrelated style flush.
+  Services.focus.clearFocus(win1);
+  Services.focus.clearFocus(win2);
+
+  let utils1 = SpecialPowers.getDOMWindowUtils(win1);
+  restyles.win1.initial = utils1.restyleGeneration;
+
+  let utils2 = SpecialPowers.getDOMWindowUtils(win2);
+  restyles.win2.initial = utils2.restyleGeneration;
+
+  // switch back to 1st window, and snapshot elementsStyled
+  win1.focus();
+  restyles.win1.activate = utils1.restyleGeneration;
+  restyles.win2.deactivate = utils2.restyleGeneration;
+
+  // switch back to 2nd window, and snapshot elementsStyled
+  win2.focus();
+  restyles.win2.activate = utils2.restyleGeneration;
+  restyles.win1.deactivate = utils1.restyleGeneration;
+
+  is(
+    restyles.win1.activate - restyles.win1.deactivate,
+    0,
+    "No elements restyled when re-activating/deactivating a window"
+  );
+  is(
+    restyles.win2.activate - restyles.win2.deactivate,
+    0,
+    "No elements restyled when re-activating/deactivating a window"
+  );
+
+  await BrowserTestUtils.closeWindow(win1);
+  await BrowserTestUtils.closeWindow(win2);
+});