Drive: Add BatchableRequest subclass.

Drive: Add BatchableRequest subclass.

To generate batch request from each request instance, batachable request class
must publish several methods to BatchRequestClass.

BUG=451917
TEST=None

Committed: https://crrev.com/900d55c855dc055f82bc3db1cb313b3e8ae1781b
Cr-Commit-Position: refs/heads/master@{#324197}

[hirono, 2015-04-03 09:36:11]

hirono@chromium.org changed reviewers:
+ kinaba@chromium.org

[hirono, 2015-04-03 09:36:12]

PTAL, thanks!

[kinaba, 2015-04-08 00:22:14]

lgtm

[hirono, 2015-04-08 04:38:46]

The CQ bit was checked by hirono@chromium.org

[hirono, 2015-04-08 04:38:55]

On 2015/04/08 00:22:14, kinaba wrote:
> lgtm

Thank you!

[commit-bot: I haz the power, 2015-04-08 04:39:09]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1053123004/1

[commit-bot: I haz the power, 2015-04-08 08:01:49]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-04-08 08:02:49]

Patchset 1 (id:??) landed as
https://crrev.com/900d55c855dc055f82bc3db1cb313b3e8ae1781b
Cr-Commit-Position: refs/heads/master@{#324197}