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This is the 1st patch to add progress bar notification support. It contains:
1) A new progress type is added and a new optional progress value is added.
2) NotificationView creates and adds a NotificationProgressbar child view.

BUG=170924
TEST=manual test by creating a progress bar notification

Review URL: https://chromiumcodereview.appspot.com/18662006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@213287 0039d316-1c4b-4281-b951-d872f2087c98