Add PlatformLocalFrame class.

third_party/WebKit/Source/core/frame/LocalFrame.h

Index: third_party/WebKit/Source/core/frame/LocalFrame.h
diff --git a/third_party/WebKit/Source/core/frame/LocalFrame.h b/third_party/WebKit/Source/core/frame/LocalFrame.h
index 45f9220e33ba3ec265d56961cc2bd8ad8783be00..a1412887270bc1405eeb2ecd2d401bfa8d515901 100644
--- a/third_party/WebKit/Source/core/frame/LocalFrame.h
+++ b/third_party/WebKit/Source/core/frame/LocalFrame.h
@@ -36,6 +36,7 @@
 #include "core/loader/FrameLoader.h"
 #include "core/page/FrameTree.h"
 #include "core/paint/PaintPhase.h"
+#include "platform/PlatformLocalFrame.h"
 #include "platform/Supplementable.h"
 #include "platform/graphics/ImageOrientation.h"
 #include "platform/heap/Handle.h"
@@ -85,6 +86,7 @@ class WebFrameScheduler;
 extern template class CORE_EXTERN_TEMPLATE_EXPORT Supplement<LocalFrame>;
 
 class CORE_EXPORT LocalFrame final : public Frame,
+                                     public PlatformLocalFrame,
                                      public Supplementable<LocalFrame> {
   USING_GARBAGE_COLLECTED_MIXIN(LocalFrame);
 
@@ -346,6 +348,11 @@ DEFINE_TYPE_CASTS(LocalFrame,
                   localFrame,
                   localFrame->IsLocalFrame(),
                   localFrame.IsLocalFrame());
+DEFINE_TYPE_CASTS(LocalFrame,
+                  PlatformLocalFrame,
+                  platform_local_frame,
+                  platform_local_frame->IsLocalFrame(),
+                  platform_local_frame.IsLocalFrame());
 
 DECLARE_WEAK_IDENTIFIER_MAP(LocalFrame);