Introduce the abstract class WebViewBase, to decouple WebViewImpl.

third_party/WebKit/Source/web/DevToolsEmulator.h

Index: third_party/WebKit/Source/web/DevToolsEmulator.h
diff --git a/third_party/WebKit/Source/web/DevToolsEmulator.h b/third_party/WebKit/Source/web/DevToolsEmulator.h
index 4dd0e9917c3f10dc6ee655d788533e7219cc012e..b8c738f5ec13cc4284bcb47dd3c080492a9aad81 100644
--- a/third_party/WebKit/Source/web/DevToolsEmulator.h
+++ b/third_party/WebKit/Source/web/DevToolsEmulator.h
@@ -21,13 +21,13 @@ class IntPoint;
 class IntRect;
 class TransformationMatrix;
 class WebInputEvent;
-class WebViewImpl;
+class WebViewBase;
 
 class WEB_EXPORT DevToolsEmulator final
     : public GarbageCollectedFinalized<DevToolsEmulator> {
  public:
   ~DevToolsEmulator();
-  static DevToolsEmulator* Create(WebViewImpl*);
+  static DevToolsEmulator* Create(WebViewBase*);
   DECLARE_TRACE();
 
   // Settings overrides.
@@ -65,7 +65,7 @@ class WEB_EXPORT DevToolsEmulator final
   WTF::Optional<IntRect> VisibleContentRectForPainting() const;
 
  private:
-  explicit DevToolsEmulator(WebViewImpl*);
+  explicit DevToolsEmulator(WebViewBase*);
 
   void EnableMobileEmulation();
   void DisableMobileEmulation();
@@ -78,7 +78,7 @@ class WEB_EXPORT DevToolsEmulator final
   void ApplyViewportOverride(TransformationMatrix*);
   void UpdateRootLayerTransform();
 
-  WebViewImpl* web_view_impl_;
+  WebViewBase* web_view_impl_;
 
   bool device_metrics_enabled_;
   bool emulate_mobile_enabled_;