Removes unnecessary preferred_size change event.

This preferred_size change invokes re-layouting the whole bubble
which causes the layout error in a really complicated code path.

This PreferredSizeChanged() seems unnecessary at all.

BUG=314218
R=stevenjb@chromium.org
TEST=manually

Review URL: https://codereview.chromium.org/99203007

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239371 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239371
Wire up the UserAvatarImage cloud policy

This CL wires up the UserAvatarImage cloud policy so that UserManager
honors it by fetching and applying a policy-set image. The UI is also
made aware of the policy, closing the image picker shown after first
login when the policy is set and preventing the user from changing the
image via chrome://settings

BUG=152957,152959
TEST=Full browser test coverage

Review URL: https://codereview.chromium.org/99373003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239372 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239372