Restore FileSystemProviderApiTest.BigFile.

Restore FileSystemProviderApiTest.BigFile.

This test is not more flaky than other tests. There seem to be some test
launching issue. Sometimes api tests do not start from time to time. It's
not common though.

Enabling the test, as it's better to have flaky test than no test. The issue
with launching tests is tracked separately.

TEST=browser_tests: *FileSystemProviderApiTest.BigFile*
BUG=458122
Committed: https://crrev.com/fae5f10535ecd3215d1e924505301562ed49744a
Cr-Commit-Position: refs/heads/master@{#316429}

[mtomasz, 2015-02-16 02:18:55]

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

[mtomasz, 2015-02-16 02:19:03]

@hirono: PTAL. Thanks.

[hirono, 2015-02-16 05:00:32]

lgtm

[mtomasz, 2015-02-16 05:00:42]

The CQ bit was checked by mtomasz@chromium.org

[commit-bot: I haz the power, 2015-02-16 05:01:17]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/925213002/1

[commit-bot: I haz the power, 2015-02-16 05:03:31]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-02-16 05:04:23]

Patchset 1 (id:??) landed as
https://crrev.com/fae5f10535ecd3215d1e924505301562ed49744a
Cr-Commit-Position: refs/heads/master@{#316429}

[flackr, 2015-02-23 17:08:05]

A revert of this CL (patchset #1 id:1) has been created in
https://codereview.chromium.org/952623002/ by flackr@chromium.org.

The reason for reverting is: FileSystemProviderApiTest.BigFile is still failing,
about 98% of runs on cros_trunk bot..