Oilpan: fix build after r192098.

Source/core/inspector/InspectorOverlayImpl.h

Index: Source/core/inspector/InspectorOverlayImpl.h
diff --git a/Source/core/inspector/InspectorOverlayImpl.h b/Source/core/inspector/InspectorOverlayImpl.h
index 29ed60e179b76ea693fdb45e93efa7f762669d87..d8476fbcf675aa442fd617d877877b8fdd562742 100644
--- a/Source/core/inspector/InspectorOverlayImpl.h
+++ b/Source/core/inspector/InspectorOverlayImpl.h
@@ -55,8 +55,9 @@ class PlatformKeyboardEvent;
 class PlatformMouseEvent;
 class PlatformTouchEvent;
 
-class InspectorOverlayImpl final : public InspectorOverlay, public InspectorOverlayHost::Listener {
+class InspectorOverlayImpl final : public NoBaseWillBeGarbageCollectedFinalized<InspectorOverlayImpl>, public InspectorOverlay, public InspectorOverlayHost::Listener {
     WTF_MAKE_FAST_ALLOCATED_WILL_BE_REMOVED;
+    WILL_BE_USING_GARBAGE_COLLECTED_MIXIN(InspectorOverlayImpl);
 public:
     class Client {
     public: