Chromecast: use CastContent{Browser,Renderer}Client as a base class.

chromecast/browser/cast_content_browser_client.h

Index: chromecast/browser/cast_content_browser_client.h
diff --git a/chromecast/browser/cast_content_browser_client.h b/chromecast/browser/cast_content_browser_client.h
index f15537a1fd5dfe7a4cde100ec1d7151f593cb0b3..e1bbe68325331d6f4effeb96ceefa26bb9b41d5c 100644
--- a/chromecast/browser/cast_content_browser_client.h
+++ b/chromecast/browser/cast_content_browser_client.h
@@ -42,7 +42,10 @@ class URLRequestContextFactory;
 
 class CastContentBrowserClient: public content::ContentBrowserClient {
  public:
-  CastContentBrowserClient();
+  // Creates an implementation of CastContentBrowserClient. Platform should
+  // link in an implementation as needed.
+  static scoped_ptr<CastContentBrowserClient> Create();
+
   ~CastContentBrowserClient() override;
 
   // Appends extra command line arguments before launching a new process.
@@ -119,6 +122,9 @@ class CastContentBrowserClient: public content::ContentBrowserClient {
       content::WebContents* web_contents) override;
 #endif  // defined(OS_ANDROID) && defined(VIDEO_HOLE)
 
+ protected:
+  CastContentBrowserClient();
+
  private:
   void AddNetworkHintsMessageFilter(int render_process_id,
                                     net::URLRequestContext* context);