Fix crash in 2D canvas caused by failed GPU context restoration

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 905 matching lines @@
   DCHECK(isAccelerated() || isHibernating() || m_softwareRenderingWhileHidden);
 
   // if hibernating but not hidden, we want to wake up from
   // hibernation
   if ((isHibernating() || m_softwareRenderingWhileHidden) && isHidden())
     return false;
 
   // If the context is lost, we don't know if we should be producing GPU or
   // software frames, until we get a new context, since the compositor will
   // be trying to get a new context and may change modes.
-  if (m_contextProvider->contextGL()->GetGraphicsResetStatusKHR() !=
-      GL_NO_ERROR)
+  if (!m_contextProvider ||
+      m_contextProvider->contextGL()->GetGraphicsResetStatusKHR() !=
+          GL_NO_ERROR)
     return false;
 
   sk_sp<SkImage> image =
       newImageSnapshot(PreferAcceleration, SnapshotReasonUnknown);
   if (!image || !image->getTexture())
     return false;
 
   // Early exit if canvas was not drawn to since last prepareMailbox.
   GLenum filter = getGLFilter();
   if (image->uniqueID() == m_lastImageId && filter == m_lastFilter)
@@ skipping 203 matching lines @@
     default;
 
 void Canvas2DLayerBridge::Logger::reportHibernationEvent(
     HibernationEvent event) {
   DEFINE_STATIC_LOCAL(EnumerationHistogram, hibernationHistogram,
                       ("Canvas.HibernationEvents", HibernationEventCount));
   hibernationHistogram.count(event);
 }
 
 }  // namespace blink