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

chromecast/browser/cast_content_browser_client.cc

Index: chromecast/browser/cast_content_browser_client.cc
diff --git a/chromecast/browser/cast_content_browser_client.cc b/chromecast/browser/cast_content_browser_client.cc
index 6578a4fe49f08950df899fe11cfafc7fb3c85f7e..a43f5d8116f7dd27032a3d51e6d5a69a8685dc6a 100644
--- a/chromecast/browser/cast_content_browser_client.cc
+++ b/chromecast/browser/cast_content_browser_client.cc
@@ -73,6 +73,11 @@ void CastContentBrowserClient::RenderProcessWillLaunch(
       new media::CmaMessageFilterHost(host->GetID()));
   host->AddFilter(cma_message_filter.get());
 #endif  // !defined(OS_ANDROID)
+
+  auto extra_filters = PlatformGetBrowserMessageFilters();
+  for (auto const& filter : extra_filters) {
+    host->AddFilter(filter.get());
+  }
 }
 
 net::URLRequestContextGetter* CastContentBrowserClient::CreateRequestContext(