Move PinchViewport to the Oilpan heap.

Source/core/frame/FrameHost.cpp

Index: Source/core/frame/FrameHost.cpp
diff --git a/Source/core/frame/FrameHost.cpp b/Source/core/frame/FrameHost.cpp
index 8e5541d66473281e0c132871f36886729ad4a9b4..45f7d1cfd3177d19ee2ddf062aca9a06c4214a92 100644
--- a/Source/core/frame/FrameHost.cpp
+++ b/Source/core/frame/FrameHost.cpp
@@ -45,7 +45,7 @@ PassOwnPtrWillBeRawPtr<FrameHost> FrameHost::create(Page& page)
 
 FrameHost::FrameHost(Page& page)
     : m_page(&page)
-    , m_pinchViewport(adoptPtr(new PinchViewport(*this)))
+    , m_pinchViewport(PinchViewport::create(*this))
     , m_eventHandlerRegistry(adoptPtrWillBeNoop(new EventHandlerRegistry(*this)))
 {
 }
@@ -88,6 +88,7 @@ EventHandlerRegistry& FrameHost::eventHandlerRegistry() const
 void FrameHost::trace(Visitor* visitor)
 {
     visitor->trace(m_page);
+    visitor->trace(m_pinchViewport);
     visitor->trace(m_eventHandlerRegistry);
 }