Move the Widget hierarchy to the Oilpan heap.

Source/core/plugins/PluginView.h

Index: Source/core/plugins/PluginView.h
diff --git a/Source/core/plugins/PluginView.h b/Source/core/plugins/PluginView.h
index b7af6c68a45b66ada177df45b1c06c343e204adc..87b42283a9b8cb5f2db52cb52bdbed5d1530b7b8 100644
--- a/Source/core/plugins/PluginView.h
+++ b/Source/core/plugins/PluginView.h
@@ -40,6 +40,7 @@ namespace blink {
 
 class ResourceError;
 class ResourceResponse;
+class ScriptController;
 class Scrollbar;
 
 class PluginView : public Widget {
@@ -59,6 +60,8 @@ public:
     virtual void didFinishLoading() { }
     virtual void didFailLoading(const ResourceError&) { }
 
+    virtual void dispose() { }
+
 protected:
     PluginView() : Widget() { }
 };