[Android] Enable Chromium command line support

Add the mechanism to support the Chromium command line in xwalk.
1 Read commands from the command line file which locates in assets
in xwalk core.
2 Expose the option to set the Chromium command line in make_apk.py.

BUG=XWALK-1269
(Cherry picked from commit 82329ede65a2dbbcd9bea09f7fd6330e726c37ed)