Move the responsibility to convert from JSON to AccountMetadata into gdata_wapi_operations.

Move the responsibility to convert from JSON to AccountMetadata into gdata_wapi_operations.

These are two purposes of this change.
1) Resolve the asymmetricity of the JSON(or XML) and typed C++ conversion.
Now, operation classes take the C++ parameters and format them into JSON/XML.
However, the response is converted in GDataWapiService. This CL resolves the
asymmetricity for AccountMetadataFeed.
2) This is also the preparation of the GDataWapiService::GetAboutResource and
GetAppList implementation.

BUG=174237
TEST=Ran unit_tests.


Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=185491

[hidehiko, 2013-02-28 13:18:41]

Thank you for your review in advance,
- hidehiko

[kinaba, 2013-03-01 00:56:49]

lgtm

[hashimoto, 2013-03-01 03:28:04]

lgtm

[commit-bot: I haz the power, 2013-03-01 03:58:26]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/hidehiko@chromium.org/12388017/1

[commit-bot: I haz the power, 2013-03-01 07:54:28]

Change committed as 185491