[Aura] Turns on Window opacity support.
[Aura] Turns on Window opacity support.

BUG=98308
TEST=None. Wait until app list window is checked in to verify.


Review URL: http://codereview.chromium.org/8383022

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@107138 0039d316-1c4b-4281-b951-d872f2087c98

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