[Android] Only force enabling WebGL for Android on IA.

We've tested the WebGL conformance test and it's very good. For other
platforms, just follow up the behaviors defined by Chromium upstream
to avoid crashes.

BUG=https://crosswalk-project.org/jira/browse/XWALK-934

It's cherry-picked from faf53c719e.
Merge pull request #1576 from yongsheng/c4-fix934

[Android] Only force enabling WebGL for Android on IA.