Fix FakeDriveService's behavior to be more correct.

Fix FakeDriveService's behavior to be more correct.

The current implementation works correctly only for the tested cases.
This patch fixes the following broken cases.
- Uploading a new file to the root collection
- Uploading onto an existing file without caring etag.

BUG=225649
Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=191799

[kinaba, 2013-04-02 05:11:30]

ptal.

I want to include this,
for using real DriveUploader instead of FakeUploader in DriveFileSystemTest,
which allows uploader to be a private member of Scheduler,
which is necessary for Scheduler to track all the upload/download traffic.

[hidehiko, 2013-04-02 05:15:07]

lgtm

[commit-bot: I haz the power, 2013-04-02 05:33:36]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/kinaba@chromium.org/13436003/1

[kinaba, 2013-04-02 07:53:07]

Committed patchset #1 manually as r191799 (presubmit successful).