Check for main frame existence in VisualViewport::setScaleAndLocation.

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

 /*
  * Copyright (C) 2013 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:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 177 matching lines @@
     setLocation(m_offset + delta);
 }
 
 void VisualViewport::setScale(float scale)
 {
     setScaleAndLocation(scale, m_offset);
 }
 
 void VisualViewport::setScaleAndLocation(float scale, const FloatPoint& location)
 {
+    if (!mainFrame())
+        return;
+
     bool valuesChanged = false;
 
     if (scale != m_scale) {
         m_scale = scale;
         valuesChanged = true;
         frameHost().chromeClient().pageScaleFactorChanged();
     }
 
     FloatPoint clampedOffset(clampOffsetToBoundaries(location));
 
     if (clampedOffset != m_offset) {
         m_offset = clampedOffset;
         scrollAnimator()->setCurrentPosition(m_offset);
 
         // SVG runs with accelerated compositing disabled so no ScrollingCoordinator.
         if (ScrollingCoordinator* coordinator = frameHost().page().scrollingCoordinator())
             coordinator->scrollableAreaScrollLayerDidChange(this);
 
-        Document* document = mainFrame()->document();
-        document->enqueueScrollEventForNode(document);
+        if (Document* document = mainFrame()->document())
+            document->enqueueScrollEventForNode(document);
 
         mainFrame()->loader().client()->didChangeScrollOffset();
         valuesChanged = true;
     }
 
     if (!valuesChanged)
         return;
 
     InspectorInstrumentation::didUpdateLayout(mainFrame());
     mainFrame()->loader().saveScrollState();
@@ skipping 508 matching lines @@
     } else if (graphicsLayer == m_rootTransformLayer) {
         name =  "Root Transform Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace blink