MediaStream API: Enhance MediaStreamDescriptor add/remove component
This patch allows the embedder to build up a MediaStreamDescriptor before announcing it to JS.
Also made a bit of refactoring to clean up the code in this area.

Patch partly covered by Blink layout tests and partly by existing and soon to land content_unittests and content_browsertests.

Review URL: https://chromiumcodereview.appspot.com/14314003

git-svn-id: svn://svn.chromium.org/blink/trunk@148731 bbb929c8-8fbe-4397-9dbb-9b2b20218538
2 files changed