[Push] Use proper accessors for PushMessagingApplicationId.

[Push] Use proper accessors for PushMessagingApplicationId.

The current design is violating the coding style (public member
variables) and is breaking some implicit functions used by some
STL implementations.

BUG=443228
Committed: https://crrev.com/e9c5cfd4faaac1aab890dba81c2423126eee64ee
Cr-Commit-Position: refs/heads/master@{#316576}

[mlamouri (slow - plz ping), 2015-02-17 12:32:30]

mlamouri@chromium.org changed reviewers:
+ johnme@chromium.org

[johnme, 2015-02-17 12:42:06]

lgtm with nit

https://codereview.chromium.org/931113003/diff/1/chrome/browser/services/gcm/...
File chrome/browser/services/gcm/push_messaging_application_id.h (right):

https://codereview.chromium.org/931113003/diff/1/chrome/browser/services/gcm/...
chrome/browser/services/gcm/push_messaging_application_id.h:73: std::string
app_id_guid_;
I'd rather you keep this immutable (const)

[mlamouri (slow - plz ping), 2015-02-17 12:47:59]

New patchsets have been uploaded after l-g-t-m from johnme@chromium.org

[mlamouri (slow - plz ping), 2015-02-17 12:48:00]

The CQ bit was checked by mlamouri@chromium.org

[commit-bot: I haz the power, 2015-02-17 12:48:32]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/931113003/20001

[commit-bot: I haz the power, 2015-02-17 13:00:56]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2015-02-17 13:00:57]

Try jobs failed on following builders:
  linux_chromium_gn_dbg on tryserver.chromium.linux (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.linux/builders/linux_chromium_...)

[mlamouri (slow - plz ping), 2015-02-17 13:56:08]

The CQ bit was checked by mlamouri@chromium.org

[commit-bot: I haz the power, 2015-02-17 13:57:19]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/931113003/40001

[commit-bot: I haz the power, 2015-02-17 14:40:26]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-02-17 14:41:31]

Patchset 3 (id:??) landed as
https://crrev.com/e9c5cfd4faaac1aab890dba81c2423126eee64ee
Cr-Commit-Position: refs/heads/master@{#316576}