[Android] Disable disambiguation popup for multiple targets.

XWalk does not use the disambiguation popup when tapping on multiple targets, so
set the renderer prefs to disable it, which is the legacy way of content API.

BUG=https://github.com/crosswalk-project/crosswalk/issues/833
Merge pull request #834 from sqliu/disable-disambiguation

[Android] Disable disambiguation popup for multiple targets.