Use new keyboard icon for Android keyboard toggle button

Since the icon does not work well with light themes, this CL specifies
Holo Dark theme for the app, instead of the device default.

Also removed text next to icons, as the keyboard icon does not have
sufficient padding. The icon is descriptive enough in itself, and the
text appears anyway if you long-press the buttons.

BUG=338773
NOTRY=true

Review URL: https://codereview.chromium.org/180703002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@253372 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 253372