scheduler: Don't throttle 0x0 frames

third_party/WebKit/Source/core/frame/FrameView.cpp

 /*
  * Copyright (C) 1998, 1999 Torben Weis <weis@kde.org>
  *                     1999 Lars Knoll <knoll@kde.org>
  *                     1999 Antti Koivisto <koivisto@kde.org>
  *                     2000 Dirk Mueller <mueller@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
@@ skipping 4235 matching lines @@
     for (Frame* child = m_frame->tree().firstChild(); child; child = child->tree().nextSibling()) {
         if (!child->isLocalFrame())
             continue;
         if (FrameView* view = toLocalFrame(child)->view())
             view->updateViewportIntersectionsForSubtree(targetState);
     }
 }
 
 void FrameView::updateThrottlingStatus()
 {
-    // Only offscreen frames can be throttled.
+    // Only offscreen frames can be throttled. Note that we disallow throttling
+    // of 0x0 frames because some sites use them to drive UI logic.
     DCHECK(m_viewportIntersectionValid);
-    m_hiddenForThrottling = m_viewportIntersection.isEmpty();
+    m_hiddenForThrottling = m_viewportIntersection.isEmpty() && !frameRect().isEmpty();
 
     // We only throttle the rendering pipeline in cross-origin frames. This is
     // to avoid a situation where an ancestor frame directly depends on the
     // pipeline timing of a descendant and breaks as a result of throttling.
     // The rationale is that cross-origin frames must already communicate with
     // asynchronous messages, so they should be able to tolerate some delay in
     // receiving replies from a throttled peer.
     //
     // Check if we can access our parent's security origin.
     m_crossOriginForThrottling = false;
@@ skipping 77 matching lines @@
 }
 
 bool FrameView::canThrottleRendering() const
 {
     if (!RuntimeEnabledFeatures::renderingPipelineThrottlingEnabled())
         return false;
     return m_subtreeThrottled || (m_hiddenForThrottling && m_crossOriginForThrottling);
 }
 
 } // namespace blink