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

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

Index: third_party/WebKit/Source/core/frame/VisualViewport.cpp
diff --git a/third_party/WebKit/Source/core/frame/VisualViewport.cpp b/third_party/WebKit/Source/core/frame/VisualViewport.cpp
index 4f8a31d369deb4a418d85e9ba9f93995e69a8c0c..bb36c38b28cf86f35aa94393c07071fa19d88ec7 100644
--- a/third_party/WebKit/Source/core/frame/VisualViewport.cpp
+++ b/third_party/WebKit/Source/core/frame/VisualViewport.cpp
@@ -334,6 +334,10 @@ void VisualViewport::attachToLayerTree(GraphicsLayer* currentLayerTreeRoot, Grap
 
 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());