Move the Widget hierarchy to the Oilpan heap.

Source/core/plugins/PluginOcclusionSupport.cpp

Index: Source/core/plugins/PluginOcclusionSupport.cpp
diff --git a/Source/core/plugins/PluginOcclusionSupport.cpp b/Source/core/plugins/PluginOcclusionSupport.cpp
index 6f47f80ee8f82d7f695f7eef5da072704e6815af..2e7c0b8b86aded2b00de57c990c61921c1dcc2f8 100644
--- a/Source/core/plugins/PluginOcclusionSupport.cpp
+++ b/Source/core/plugins/PluginOcclusionSupport.cpp
@@ -164,13 +164,13 @@ void getPluginOcclusions(Element* element, Widget* parentWidget, const IntRect&
     FrameView* parentFrameView = toFrameView(parentWidget);
 
     // Occlusions by iframes.
-    const HashSet<RefPtr<Widget> >* children = parentFrameView->children();
-    for (HashSet<RefPtr<Widget> >::const_iterator it = children->begin(); it != children->end(); ++it) {
+    const WillBeHeapHashSet<RefPtrWillBeMember<Widget> >* children = parentFrameView->children();
+    for (WillBeHeapHashSet<RefPtrWillBeMember<Widget> >::const_iterator it = children->begin(); it != children->end(); ++it) {
         // We only care about FrameView's because iframes show up as FrameViews.
         if (!(*it)->isFrameView())
             continue;
 
-        const FrameView* frameView = toFrameView((*it).get());
+        const FrameView* frameView = toFrameView(it->get());
         // Check to make sure we can get both the element and the RenderObject
         // for this FrameView, if we can't just move on to the next object.
         // FIXME: Plugin occlusion by remote frames is probably broken.