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This listener uses the ImageCapture API to watch for attach and detach
events of PTP devices and other devices which can be read through the
library. It forwards such notifications through the SystemMonitor.

Also provides an API for clients to access such devices directly and
retrieve the media contents from them.

R=thestig@chromium.org,sail@chromium.org
BUG=151681


Review URL: https://chromiumcodereview.appspot.com/11442057

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@175471 0039d316-1c4b-4281-b951-d872f2087c98