Reland: Show the eject button only for removables and file handlers.

Reland: 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.

TBR=benwells@chromium.org
TEST=browser_tests: *OnVolumeListChanged*
BUG=440674
Committed: https://crrev.com/c314676fbb9b81b7450aeec1a803b872a2f34f2a
Cr-Commit-Position: refs/heads/master@{#330073}

[mtomasz, 2015-05-15 08:51:13]

Patchset #1 (id:1) has been deleted

[mtomasz, 2015-05-15 08:54:23]

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

[mtomasz, 2015-05-15 09:14:34]

https://codereview.chromium.org/1146463002/diff/20001/chrome/browser/extensio...
File chrome/browser/extensions/api/file_system/file_system_api.cc (right):

https://codereview.chromium.org/1146463002/diff/20001/chrome/browser/extensio...
chrome/browser/extensions/api/file_system/file_system_api.cc:322: new
ConsentProviderDelegate(profile, nullptr));
This was causing a leak, as the delegate is not owned by ContentProvider.

[hirono, 2015-05-15 09:29:03]

lgtm

[mtomasz, 2015-05-15 09:32:01]

Thanks!

[mtomasz, 2015-05-15 09:32:06]

The CQ bit was checked by mtomasz@chromium.org

[commit-bot: I haz the power, 2015-05-15 09:32:11]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1146463002/30001

[commit-bot: I haz the power, 2015-05-15 10:48:16]

Committed patchset #2 (id:30001)

[commit-bot: I haz the power, 2015-05-15 10:49:06]

Patchset 2 (id:??) landed as
https://crrev.com/c314676fbb9b81b7450aeec1a803b872a2f34f2a
Cr-Commit-Position: refs/heads/master@{#330073}