Replacing const by value return values into const by ref in chrome/browser/extensions/api/identity

Replacing const by value return values into const by ref in chrome/browser/extensions/api/identity

Returning a const reference to an object instead of a copy.
Returning a reference to an instance that's still in scope when the function returns, then it will be faster, as no copy of the oject is being created.
This CL turns const by value return values into const by ref

BUG=393155
Committed: https://crrev.com/8c96177b61a9dbb176a82b1732b41dd0154336b7
Cr-Commit-Position: refs/heads/master@{#327682}

[payal.pandey, 2015-04-29 11:36:32]

payal.pandey@samsung.com changed reviewers:
+ jochen@chromium.org

[payal.pandey, 2015-04-29 11:36:32]

Please have a look, Thanks.

[payal.pandey, 2015-04-29 11:36:36]

Please have a look, Thanks.

[payal.pandey, 2015-04-29 18:21:17]

payal.pandey@samsung.com changed reviewers:
+ courage@chromium.org

[jochen (gone - plz use gerrit), 2015-04-30 07:16:36]

lgtm

[payal.pandey, 2015-04-30 07:21:00]

The CQ bit was checked by payal.pandey@samsung.com

[commit-bot: I haz the power, 2015-04-30 07:21:27]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1116633003/1

[commit-bot: I haz the power, 2015-04-30 08:08:02]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-30 08:08:56]

Patchset 1 (id:??) landed as
https://crrev.com/8c96177b61a9dbb176a82b1732b41dd0154336b7
Cr-Commit-Position: refs/heads/master@{#327682}