Introduce the abstract class WebViewBase, to decouple WebViewImpl.

third_party/WebKit/Source/web/WebLocalFrameImpl.h

Index: third_party/WebKit/Source/web/WebLocalFrameImpl.h
diff --git a/third_party/WebKit/Source/web/WebLocalFrameImpl.h b/third_party/WebKit/Source/web/WebLocalFrameImpl.h
index cf1f229ebd2d98377ee9839e46b095d6ccf58bd3..adef6197aef77dec8b92aec08ec977ca77bd7b72 100644
--- a/third_party/WebKit/Source/web/WebLocalFrameImpl.h
+++ b/third_party/WebKit/Source/web/WebLocalFrameImpl.h
@@ -73,7 +73,7 @@ class WebPlugin;
 class WebPluginContainerImpl;
 class WebScriptExecutionCallback;
 class WebView;
-class WebViewImpl;
+class WebViewBase;
 enum class WebFrameLoadType;
 struct FrameLoadRequest;
 struct WebContentSecurityPolicyViolation;
@@ -365,7 +365,7 @@ class WEB_EXPORT WebLocalFrameImpl final
   static WebPluginContainerImpl* CurrentPluginContainer(LocalFrame*,
                                                         Node* = nullptr);
 
-  WebViewImpl* ViewImpl() const;
+  WebViewBase* ViewImpl() const;
 
   FrameView* GetFrameView() const {
     return GetFrame() ? GetFrame()->View() : 0;