Introduce WebRemoteFrameBase to break dependencies on WebRemoteFrameImpl.

third_party/WebKit/Source/core/page/ChromeClient.h

Index: third_party/WebKit/Source/core/page/ChromeClient.h
diff --git a/third_party/WebKit/Source/core/page/ChromeClient.h b/third_party/WebKit/Source/core/page/ChromeClient.h
index c709d97f990df18f92e0e31e357ce37658367804..6911fe640cf35dd7d3583a9972602e0600e249b2 100644
--- a/third_party/WebKit/Source/core/page/ChromeClient.h
+++ b/third_party/WebKit/Source/core/page/ChromeClient.h
@@ -73,12 +73,14 @@ class LocalFrame;
 class Node;
 class Page;
 class PopupOpeningObserver;
+class RemoteFrame;
 class WebDragData;
 class WebFrameScheduler;
 class WebImage;
 class WebLayer;
 class WebLayerTreeView;
 class WebLocalFrameBase;
+class WebRemoteFrameBase;
 
 struct CompositedSelection;
 struct DateTimeChooserParameters;
@@ -358,6 +360,10 @@ class CORE_EXPORT ChromeClient : public PlatformChromeClient {
     return nullptr;
   }
 
+  virtual WebRemoteFrameBase* GetWebRemoteFrameBase(RemoteFrame&) {
+    return nullptr;
+  }
+
   DECLARE_TRACE();
 
  protected: