Bug 1742797 - Discard WebRender resources when popup hides. r=Gijs,emilio

The browser test in this change was originally written by Gijs.

Differential Revision: https://phabricator.services.mozilla.com/D134444

browser/base/content/test/performance/browser.ini

@@ -30,6 +30,9 @@ skip-if =
   debug
   (os == 'win') # Win32 because of intermittent OOM failures, bug 1533141 for aarch64, Bug 1775626
   (os == 'linux' && socketprocess_networking) # Bug 1382809, bug 1369959
+[browser_panel_vsync.js]
+support-files =
+  !/browser/components/downloads/test/browser/head.js
 [browser_preferences_usage.js]
 https_first_disabled = true
 skip-if =

browser/base/content/test/performance/browser_panel_vsync.js

@@ -0,0 +1,59 @@
+/* Any copyright is dedicated to the Public Domain.
+   http://creativecommons.org/publicdomain/zero/1.0/ */
+/* import-globals-from ../../../../components/downloads/test/browser/head.js */
+
+"use strict";
+
+Services.scriptloader.loadSubScript(
+  "chrome://mochitests/content/browser/browser/components/downloads/test/browser/head.js",
+  this
+);
+
+add_task(
+  async function test_opening_panel_and_closing_should_not_leave_vsync() {
+    await SpecialPowers.pushPrefEnv({
+      set: [["browser.download.autohideButton", false]],
+    });
+    await promiseButtonShown("downloads-button");
+
+    const downloadsButton = document.getElementById("downloads-button");
+    const shownPromise = promisePanelOpened();
+    EventUtils.synthesizeNativeMouseEvent({
+      type: "click",
+      target: downloadsButton,
+      atCenter: true,
+    });
+    await shownPromise;
+
+    is(DownloadsPanel.panel.state, "open", "Check that panel state is 'open'");
+
+    await TestUtils.waitForCondition(
+      () => !ChromeUtils.vsyncEnabled(),
+      "Make sure vsync disabled"
+    );
+    // Should not already be using vsync
+    ok(!ChromeUtils.vsyncEnabled(), "vsync should be off initially");
+
+    const hiddenPromise = BrowserTestUtils.waitForEvent(
+      DownloadsPanel.panel,
+      "popuphidden"
+    );
+    EventUtils.synthesizeNativeMouseEvent({
+      type: "click",
+      target: downloadsButton,
+      atCenter: true,
+    });
+
+    await Promise.all([
+      hiddenPromise,
+      TestUtils.waitForCondition(() => !ChromeUtils.vsyncEnabled()),
+    ]);
+
+    ok(!ChromeUtils.vsyncEnabled(), "vsync should still be off");
+    is(
+      DownloadsPanel.panel.state,
+      "closed",
+      "Check that panel state is 'closed'"
+    );
+  }
+);

layout/xul/nsMenuPopupFrame.cpp

@@ -1098,6 +1098,10 @@ void nsMenuPopupFrame::HidePopup(bool aDeselectMenu, nsPopupState aNewState) {
   mCurrentMenu = nullptr;  // make sure no current menu is set
   mHFlip = mVFlip = false;
 
+  if (auto* widget = GetWidget()) {
+    widget->ClearCachedWebrenderResources();
+  }
+
   nsView* view = GetView();
   nsViewManager* viewManager = view->GetViewManager();
   viewManager->SetViewVisibility(view, nsViewVisibility_kHide);