Add chrome.fileManagerPrivate.getProvidingExtensions().

Add chrome.fileManagerPrivate.getProvidingExtensions().

This method returns a list of installed providing extensions with extra flags
saying whether the extension handles configuring or adding new mount points
via an event.

TEST=Not yet, they will be added in a follow up CL once all is wired up.
BUG=474146
Committed: https://crrev.com/6cac9ef5b1487d39477e453d270de321d6db8b87
Cr-Commit-Position: refs/heads/master@{#325395}

[mtomasz, 2015-04-15 07:07:21]

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

[mtomasz, 2015-04-15 07:07:41]

@isherman: PTAL at histograms.
@hirono: PTAL at everything else.

Thanks.

[hirono, 2015-04-15 07:44:18]

lgtm. Please update the master of closure compiler's externs.

https://codereview.chromium.org/1089193002/diff/1/chrome/browser/chromeos/ext...
File chrome/browser/chromeos/extensions/file_manager/private_api_misc.cc
(right):

https://codereview.chromium.org/1089193002/diff/1/chrome/browser/chromeos/ext...
chrome/browser/chromeos/extensions/file_manager/private_api_misc.cc:467: return
RespondNow(OneArgument(new base::FundamentalValue(true)));
Thank you for fixing this!

[Ilya Sherman, 2015-04-15 20:50:21]

LGTM

[mtomasz, 2015-04-16 03:09:10]

The CQ bit was checked by mtomasz@chromium.org

[mtomasz, 2015-04-16 03:09:10]

The patchset sent to the CQ was uploaded after l-g-t-m from hirono@chromium.org,
isherman@chromium.org
Link to the patchset: https://codereview.chromium.org/1089193002/#ps20001
(title: "Rebased.")

[commit-bot: I haz the power, 2015-04-16 03:09:39]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1089193002/20001

[commit-bot: I haz the power, 2015-04-16 04:57:32]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-04-16 04:58:28]

Patchset 2 (id:??) landed as
https://crrev.com/6cac9ef5b1487d39477e453d270de321d6db8b87
Cr-Commit-Position: refs/heads/master@{#325395}