Bug 1742797 - Address review comment and ignore spurious popuphiding events on Linux r=mconley

Differential Revision: https://phabricator.services.mozilla.com/D151622

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

@@ -34,6 +34,21 @@ add_task(
     // Should not already be using vsync
     ok(!ChromeUtils.vsyncEnabled(), "vsync should be off initially");
 
+    if (
+      AppConstants.platform == "linux" &&
+      DownloadsPanel.panel.state != "open"
+    ) {
+      // Panels sometime receive spurious popuphiding events on Linux.
+      // Given the main target of this test is Windows, avoid causing
+      // intermittent failures and just make the test return early.
+      todo(
+        false,
+        "panel should still be 'open', current state: " +
+          DownloadsPanel.panel.state
+      );
+      return;
+    }
+
     const hiddenPromise = BrowserTestUtils.waitForEvent(
       DownloadsPanel.panel,
       "popuphidden"

layout/xul/nsMenuPopupFrame.cpp

@@ -1099,6 +1099,9 @@ void nsMenuPopupFrame::HidePopup(bool aDeselectMenu, nsPopupState aNewState) {
   mHFlip = mVFlip = false;
 
   if (auto* widget = GetWidget()) {
+    // Ideally we should call ClearCachedWebrenderResources but there are
+    // intermittent failures (see bug 1748788), so we currently call
+    // ClearWebrenderAnimationResources instead.
     widget->ClearWebrenderAnimationResources();
   }