MediaRenderer: Returns initialization result in the init callback.
Currently the initialization result is returned in the OnError() call. However,
the init_cb is returned on the MediaRenderer pipe, while OnError() is called on
the client (MediaRendererClient) pipe. The order of these two calls are not
deterministic.
This CL makes sure the initialization result is always returned in the init
callback. This is also more consistent with the media::Renderer interface.
BUG=509801
TEST=All existing tests pass.
Review URL: https://codereview.chromium.org/
1232703005
Cr-Commit-Position: refs/heads/master@{#338581}