crosswalk-8: Merge cordova-android 3.5.1 into the tree.

3.5.1 is a security release with fixes for CVE-2014-3500, CVE-2014-3501
and CVE-2014-3502.

Instead of rebasing the tree, I have adopted a more conservative
approach and just `git merge`d the 3.5.1 tag from upstream, as both
3.5.0 and 3.5.1 have a shared history (ie. we do not _have_ to rebase).

The following adjustments had to be made to make Crosswalk fit into the
commits above:

* CordovaWebViewClient and CordovaUriHelper were changed make the new
  URI helper use XWalkView instead of WebView.

* The "Handle unsupported protocol errors in webview better"
  implementation was moved from `onReceivedError()` to
  `onReceivedLoadError()`, since the former does not exist in
  `XWalkResourceClient` (the error code was changed accordingly).

The ticket tracking this update is XWALK-2675; this merge is being done
directly to the crosswalk-8 branch because:

* We need to reach the stable channel as fast as possible because this
  is a security fix.

* Several tests in the `test/` directory are currently crashing in
  crosswalk-9 and master (ie. crosswalk-10) on both ARM and x86, so I am
  not confident this merge is enough for those branches.