[Chromecast] Clarify lifetime of CastGinRunner.

chromecast/renderer/cast_content_renderer_client.cc

Index: chromecast/renderer/cast_content_renderer_client.cc
diff --git a/chromecast/renderer/cast_content_renderer_client.cc b/chromecast/renderer/cast_content_renderer_client.cc
index b625bd956f9097761878b098986afc35920f062a..718403ab16566cfa12aa4b014cb19aae7ba56c99 100644
--- a/chromecast/renderer/cast_content_renderer_client.cc
+++ b/chromecast/renderer/cast_content_renderer_client.cc
@@ -148,8 +148,7 @@ void CastContentRendererClient::RunScriptsAtDocumentStart(
   v8::Local<v8::Context> context =
       render_frame->GetWebFrame()->mainWorldScriptContext();
 
-  // CastGinRunner manages its own lifetime.
-  CastGinRunner* runner = new CastGinRunner(render_frame);
+  CastGinRunner* runner = CastGinRunner::Get(render_frame);
   gin::Runner::Scope scoper(runner);
 
   // Initialize AMD API for Mojo.