Restrict access to Pepper MediaStream APIs to whitelisted apps.

Adds a AllowPepperMediaStreamAPI method to content::ContentRendererClient to control access to private media stream apis.
Adds an implementation to ChromeContentRendererClient which checks the URL against a whitelist containing a single extension host. This will be set to the Hangouts app's host name when it's available.

BUG=230980

Review URL: https://chromiumcodereview.appspot.com/16455010

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@207091 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/content/public/renderer/content_renderer_client.cc b/content/public/renderer/content_renderer_client.cc
index b4062de..255b89f 100644
--- a/content/public/renderer/content_renderer_client.cc
+++ b/content/public/renderer/content_renderer_client.cc
@@ -165,4 +165,8 @@
   return false;
 }
 
+bool ContentRendererClient::AllowPepperMediaStreamAPI(const GURL& url) const {
+  return false;
+}
+
 }  // namespace content