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In onAttachedToWindow, check that if the view is hardware accelerated,
then enable hardware accelerated 2d canvas. Similarly disable canvas on
detach.

Note that accelerated 2d canvas is still off by default, but this patch
adds a command line switch to turn it on.

BUG=332273

Review URL: https://codereview.chromium.org/140753006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@245648 0039d316-1c4b-4281-b951-d872f2087c98