Break dependency between ChromeClient and WebViewImpl, and ChromeClientImpl.

third_party/WebKit/Source/web/WebViewImpl.h

Index: third_party/WebKit/Source/web/WebViewImpl.h
diff --git a/third_party/WebKit/Source/web/WebViewImpl.h b/third_party/WebKit/Source/web/WebViewImpl.h
index 9a18d090efab69f9474356c79ac08ed143fa1823..ef8368e323f1bdf538da68cff7fbf473c39e308c 100644
--- a/third_party/WebKit/Source/web/WebViewImpl.h
+++ b/third_party/WebKit/Source/web/WebViewImpl.h
@@ -494,7 +494,9 @@ class WEB_EXPORT WebViewImpl final
     return last_frame_time_monotonic_;
   }
 
-  ChromeClientImpl& ChromeClient() const { return *chrome_client_impl_.Get(); }
+  class ChromeClient& ChromeClient() const override {
+    return *chrome_client_impl_.Get();
+  }
 
   // Returns the currently active WebInputMethodController which is the one
   // corresponding to the focused frame. It will return nullptr if there is no