Add the chrome.fileSystem.onVolumeListChanged event.

Add the chrome.fileSystem.onVolumeListChanged event.

This CL adds an event which notifies extension about changed list of volumes
which can be requested via chrome.fileSystem.requestFileSystem.

TEST=browser_tests: *OnVolumeListChanged*
BUG=440674
Committed: https://crrev.com/a1cc3a6222b0027a3fcf7cf31787950b0496b85f
Cr-Commit-Position: refs/heads/master@{#330047}

[mtomasz, 2015-05-13 12:57:59]

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

[mtomasz, 2015-05-13 12:58:00]

@benwells: PTAL. Thanks.

[mtomasz, 2015-05-14 10:12:09]

On 2015/05/13 12:58:00, mtomasz wrote:
> @benwells: PTAL. Thanks.

@benwells: Friendly ping. It's very important for M44, and the branch cut is
tomorrow. Sorry for leaving it until the last moment (again). Thanks.

[benwells, 2015-05-15 03:49:49]

does some feature json need to be updated for this?
lgtm

[mtomasz, 2015-05-15 03:53:21]

AFAIK, no need. All tests pass.

[mtomasz, 2015-05-15 03:53:55]

The CQ bit was checked by mtomasz@chromium.org

[commit-bot: I haz the power, 2015-05-15 03:54:20]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1135383002/20001

[benwells, 2015-05-15 03:55:56]

On 2015/05/15 03:53:21, mtomasz wrote:
> AFAIK, no need. All tests pass.

ok, on reflection that makes sense.

[commit-bot: I haz the power, 2015-05-15 05:36:49]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-05-15 05:37:25]

Patchset 2 (id:??) landed as
https://crrev.com/a1cc3a6222b0027a3fcf7cf31787950b0496b85f
Cr-Commit-Position: refs/heads/master@{#330047}

[henrika (OOO until Aug 14), 2015-05-15 08:35:15]

A revert of this CL (patchset #2 id:20001) has been created in
https://codereview.chromium.org/1145563002/ by henrika@chromium.org.

The reason for reverting is: Seems to break browser_tests failed
interactive_ui_tests on
Linux Chromium OS ASan LSan Tests (1).

This CL was the best I could find in the blame list. Reverting as Chrome sheriff
to see if it helps.

See
https://build.chromium.org/p/chromium.memory/builders/Linux%20Chromium%20OS%2....