[android] Un-delete zoom APIs.

The Zoom APIs are still needed, so partially reverting r227763.

R=joth@chromium.org, qinmin@chromium.org
TBR=joth@chromium.org

BUG=None
TEST=None

Review URL: https://codereview.chromium.org/26737002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@227793 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 227793