[GCM] Adding handling of heartbeat intervals to the GCM store.

Adding handling of heartbeat intervals to the GCM store.

Adding methods to GCMStore, GCMStoreImpl and ::Backend:
* AddHeartbeatInterval, RemoveHeartbeatInterval, for managing
  persistence, as well as
* LoadHeartbeatIntervals to load intervals at startup

Adding tests for the above.

BUG=481174
Committed: https://crrev.com/06a32f524691c4efc432d4df1736d69c24360c75
Cr-Commit-Position: refs/heads/master@{#328191}

[fgorski, 2015-05-01 21:35:17]

fgorski@chromium.org changed reviewers:
+ zea@chromium.org

[fgorski, 2015-05-01 21:35:39]

Nicolas, PTAL.

This is patch 2. I'll wire everything up in the next one.

[Nicolas Zea, 2015-05-04 17:45:28]

LGTM

https://codereview.chromium.org/1121003003/diff/20001/google_apis/gcm/engine/...
File google_apis/gcm/engine/gcm_store_impl.cc (right):

https://codereview.chromium.org/1121003003/diff/20001/google_apis/gcm/engine/...
google_apis/gcm/engine/gcm_store_impl.cc:147: std::string MakeHeartbeatKey(const
std::string& scope) {
remind me, what is the scope derived from?

[fgorski, 2015-05-04 18:14:54]

fgorski@chromium.org changed reviewers:
+ asvitkine@chromium.org

[fgorski, 2015-05-04 18:14:54]

Starting tests, adding Alexei for histograms.

https://codereview.chromium.org/1121003003/diff/20001/google_apis/gcm/engine/...
File google_apis/gcm/engine/gcm_store_impl.cc (right):

https://codereview.chromium.org/1121003003/diff/20001/google_apis/gcm/engine/...
google_apis/gcm/engine/gcm_store_impl.cc:147: std::string MakeHeartbeatKey(const
std::string& scope) {
On 2015/05/04 17:45:28, Nicolas Zea wrote:
> remind me, what is the scope derived from?

It is simply a token uniquely identifying component requesting the custom
heartbeat interval.

[Alexei Svitkine (slow), 2015-05-04 18:29:41]

lgtm

[fgorski, 2015-05-04 19:00:47]

The CQ bit was checked by fgorski@chromium.org

[commit-bot: I haz the power, 2015-05-04 19:02:38]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1121003003/20001

[commit-bot: I haz the power, 2015-05-04 21:40:57]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-05-04 21:42:02]

Patchset 2 (id:??) landed as
https://crrev.com/06a32f524691c4efc432d4df1736d69c24360c75
Cr-Commit-Position: refs/heads/master@{#328191}