[GCM] Fixing loading from GCM store after signing out of a profile
The problem was with how we write and then update the
mapping with status removing:
* first write happens immediately, without a message ID
* second write after we successfully send a message (that
one includes a message ID).
If GCM is turned off or Chrome gets shut down after the
first message, we will not be able to later turn it back
on, because reading of the mapping will fail.
R=jianli@chromium.org,zea@chromium.org
BUG=435401
Review URL: https://codereview.chromium.org/
747113002
Cr-Commit-Position: refs/heads/master@{#305300}