Provide a ScreenOrientationDispatcherHost getter.

SSIA. We need it in order to be able to set ScreenOrientationProvider
from Xwalk.
[Android] Add code path for initializing ContentReadbackHandler
ContentReadbackHandler initialization is newly added from chromium
36.0.1985. We need to init it for TextureView path to avoid crash on
destroying.

BUG=https://crosswalk-project.org/jira/browse/XWALK-1887

Reworked with M37.