[Android] Enable Web Audio on x86 -- part 3

Enable the flag to let web audio work.

Conflicts:
	content/child/runtime_features.cc

Rework with 34.0.1809.0 code base.
Revert "[Android] Enable Web Audio on x86 -- part 3"

This reverts commit af75b1265672e5de08f381f6ea923c7075caa522.

The patch is useless after rebasing, as we have already enabled
Web Audio on x86 via the command line in xwalk.
See https://github.com/crosswalk-project/crosswalk/pull/1643