[Chromecast] Moves persistent UMA client ID handling to common code.

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 e445c1e1ab0a2e46c5ccc4bf583368b6b324234c..2b4a5dff1b5f8e04bf87d13e0ecc7495abc84297 100644
--- a/chromecast/browser/cast_content_browser_client.cc
+++ b/chromecast/browser/cast_content_browser_client.cc
@@ -87,11 +87,21 @@ CastContentBrowserClient::CreateMediaPipelineBackend(
 }
 #endif
 
+void CastContentBrowserClient::SetMetricsClientId(
+    const std::string& client_id) {
+}
+
+void CastContentBrowserClient::RegisterMetricsProviders(
+    ::metrics::MetricsService* metrics_service) {
+}
+
 content::BrowserMainParts* CastContentBrowserClient::CreateBrowserMainParts(
     const content::MainFunctionParams& parameters) {
-  return new CastBrowserMainParts(parameters,
-                                  url_request_context_factory_.get(),
-                                  CreateAudioManagerFactory());
+  content::BrowserMainParts* parts = new CastBrowserMainParts(
+      parameters, url_request_context_factory_.get(),
+      CreateAudioManagerFactory());
+  CastBrowserProcess::GetInstance()->SetCastContentBrowserClient(this);
+  return parts;
 }
 
 void CastContentBrowserClient::RenderProcessWillLaunch(