[GCM] Notify the message sending status when the message is queued for sending

The ACK will only be received from the GCM when there is incoming message.
We should also report back the message sending status when the message is
queued for sending.

BUG=284553
R=fgorski@chromium.org
TBR=zea@chromium.org

Review URL: https://codereview.chromium.org/138903030

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@248316 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 248316