Return early from VisualViewport::initializeScrollbars if not attached yet.

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 316 matching lines @@
 
         initializeScrollbars();
     }
 
     m_innerViewportScrollLayer->removeAllChildren();
     m_innerViewportScrollLayer->addChild(currentLayerTreeRoot);
 }
 
 void VisualViewport::initializeScrollbars()
 {
+    // Do nothing if not attached to layer tree yet - will initialize upon attach.
+    if (!m_innerViewportContainerLayer)
+        return;
+
     if (visualViewportSuppliesScrollbars()) {
         if (!m_overlayScrollbarHorizontal->parent())
             m_innerViewportContainerLayer->addChild(m_overlayScrollbarHorizontal.get());
         if (!m_overlayScrollbarVertical->parent())
             m_innerViewportContainerLayer->addChild(m_overlayScrollbarVertical.get());
     } else {
         m_overlayScrollbarHorizontal->removeFromParent();
         m_overlayScrollbarVertical->removeFromParent();
     }
 
@@ skipping 393 matching lines @@
     } else if (graphicsLayer == m_rootTransformLayer) {
         name =  "Root Transform Layer";
     } else {
         ASSERT_NOT_REACHED();
     }
 
     return name;
 }
 
 } // namespace blink