[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
Merge pull request #1572 from yongsheng/fix934

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