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This partially addresses http://code.google.com/p/chromium/issues/detail?id=137155 by placing new notifications at the front of the list and rendering newer notifications first.
This also greatly simplifes the layout code for web notifications.
It also fixes a bug where notifications were not getting redrawn correctly when the shelf alignment was changed.

BUG=137155
TEST=New web notifications should show up at the top of the list. The list should size correctly as new notifications arrive, scrolling when the max size is reached, showing up to 99 notifications in the list.
R=sadrul@chromium.org


Review URL: https://chromiumcodereview.appspot.com/10833041

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@148991 0039d316-1c4b-4281-b951-d872f2087c98