Oilpan: Prepare moving InspectorOverlayHost to Oilpan

Source/core/inspector/PageDebuggerAgent.h

Index: Source/core/inspector/PageDebuggerAgent.h
diff --git a/Source/core/inspector/PageDebuggerAgent.h b/Source/core/inspector/PageDebuggerAgent.h
index 8f53466907d7e7375a2338b4e3a1ba583b1baf28..88a1ccd4ea0faa28fd163fc1beca0ed1e6a793b2 100644
--- a/Source/core/inspector/PageDebuggerAgent.h
+++ b/Source/core/inspector/PageDebuggerAgent.h
@@ -49,6 +49,7 @@ class PageDebuggerAgent FINAL
     , public InspectorOverlayHost::Listener {
     WTF_MAKE_NONCOPYABLE(PageDebuggerAgent);
     WTF_MAKE_FAST_ALLOCATED_WILL_BE_REMOVED;
+    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(PageDebuggerAgent);
 public:
     static PassOwnPtrWillBeRawPtr<PageDebuggerAgent> create(PageScriptDebugServer*, InspectorPageAgent*, InjectedScriptManager*, InspectorOverlay*);
     virtual ~PageDebuggerAgent();