Introduce the abstract class WebViewBase, to decouple WebViewImpl.

third_party/WebKit/Source/web/EditorClientImpl.h

Index: third_party/WebKit/Source/web/EditorClientImpl.h
diff --git a/third_party/WebKit/Source/web/EditorClientImpl.h b/third_party/WebKit/Source/web/EditorClientImpl.h
index d06df631b587c80de65480ad6c23113499f40360..d9b182f205b4a16d0415c28983ead38ad7bfa7b8 100644
--- a/third_party/WebKit/Source/web/EditorClientImpl.h
+++ b/third_party/WebKit/Source/web/EditorClientImpl.h
@@ -37,11 +37,11 @@
 namespace blink {
 
 class LocalFrame;
-class WebViewImpl;
+class WebViewBase;
 
 class EditorClientImpl final : public EditorClient {
  public:
-  explicit EditorClientImpl(WebViewImpl*);
+  explicit EditorClientImpl(WebViewBase*);
   ~EditorClientImpl() override;
 
   void RespondToChangedContents() override;
@@ -51,7 +51,7 @@ class EditorClientImpl final : public EditorClient {
   bool HandleKeyboardEvent(LocalFrame*) override;
 
  private:
-  WebViewImpl* web_view_;
+  WebViewBase* web_view_;
 };
 
 }  // namespace blink