ui/gfx: Remove gmock usage from animation_container_unittest.cc.

Rewrite part of the test using plain C++ Fake pattern.

BUG=134675
TEST=ui_unittests --gtest_filter=AnimationContainerTest.*
R=ben@chromium.org

Review URL: https://codereview.chromium.org/56193006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@233168 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 233168