Introduce the abstract class WebViewBase, to decouple WebViewImpl.

third_party/WebKit/Source/web/WebFrameWidgetBase.h

Index: third_party/WebKit/Source/web/WebFrameWidgetBase.h
diff --git a/third_party/WebKit/Source/web/WebFrameWidgetBase.h b/third_party/WebKit/Source/web/WebFrameWidgetBase.h
index a8ec733d9dcb180e4a83b3c0b01a7b7409143e9b..ef640ac314754e634c067de03da8f261a52f0703 100644
--- a/third_party/WebKit/Source/web/WebFrameWidgetBase.h
+++ b/third_party/WebKit/Source/web/WebFrameWidgetBase.h
@@ -20,7 +20,7 @@ class GraphicsLayer;
 class WebImage;
 class WebLayer;
 class WebLayerTreeView;
-class WebViewImpl;
+class WebViewBase;
 class HitTestResult;
 struct WebPoint;
 
@@ -95,7 +95,7 @@ class WebFrameWidgetBase : public WebFrameWidget {
   // Helper function to call VisualViewport::viewportToRootFrame().
   WebPoint ViewportToRootFrame(const WebPoint& point_in_viewport) const;
 
-  WebViewImpl* View() const;
+  WebViewBase* View() const;
 
   // Returns the page object associated with this widget. This may be null when
   // the page is shutting down, but will be valid at all other times.