Chromecast: add platform hooks to inject browser/renderer message filters.

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 476d6601a4f70a20d5dd89b407286ae5174ab0b4..459a3e9a2d123a8ec18eb4649766eb1e5123b4d9 100644
--- a/chromecast/browser/cast_content_browser_client.h
+++ b/chromecast/browser/cast_content_browser_client.h
@@ -15,19 +15,29 @@ namespace breakpad {
 class CrashHandlerHostLinux;
 }
 
+namespace content {
+class BrowserMessageFilter;
+}
+
 namespace chromecast {
 namespace shell {
 
 class CastBrowserMainParts;
 class URLRequestContextFactory;
 
-void PlatformAppendExtraCommandLineSwitches(base::CommandLine* command_line);
-
 class CastContentBrowserClient: public content::ContentBrowserClient {
  public:
   CastContentBrowserClient();
   ~CastContentBrowserClient() override;
 
+  // Appends extra command line arguments before launching a new process.
+  void PlatformAppendExtraCommandLineSwitches(base::CommandLine* command_line);
+
+  // Returns any BrowserMessageFilters from the platform implementation that
+  // should be added when launching a new render process.
+  std::vector<scoped_refptr<content::BrowserMessageFilter>>
+  PlatformGetBrowserMessageFilters();
+
   // content::ContentBrowserClient implementation:
   content::BrowserMainParts* CreateBrowserMainParts(
       const content::MainFunctionParams& parameters) override;