Fix 2D canvas content loss while page is hidden

third_party/WebKit/Source/platform/graphics/Canvas2DLayerBridge.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 502 matching lines @@
     if (m_layer && !m_destructionInProgress)
         checkSurfaceValid(); // To ensure rate limiter is disabled if context is lost.
     return m_contextProvider ? m_contextProvider->context3d() : 0;
 }
 
 bool Canvas2DLayerBridge::checkSurfaceValid()
 {
     ASSERT(!m_destructionInProgress);
     if (m_destructionInProgress)
         return false;
+    if (isHibernating())
+        return true;
     if (!m_layer)
         return true;
     if (!m_surface)
         return false;
     if (m_contextProvider->context3d()->isContextLost()) {
         m_surface.clear();
         for (auto mailboxInfo = m_mailboxes.begin(); mailboxInfo != m_mailboxes.end(); ++mailboxInfo) {
             if (mailboxInfo->m_image)
                 mailboxInfo->m_image.clear();
         }
@@ skipping 287 matching lines @@
     m_image = other.m_image;
     m_parentLayerBridge = other.m_parentLayerBridge;
 }
 
 void Canvas2DLayerBridge::Logger::reportHibernationEvent(HibernationEvent event)
 {
     blink::Platform::current()->histogramEnumeration("Canvas.HibernationEvents", event, HibernationEventCount);
 }
 
 } // namespace blink