[Android] Refactor Java extension system

The commit is to decouple the extension from XWalkRuntimeViewProvider
and simplify the interfaces exposed by XWalkRuntimeViewProvider. Now it
is easy to use the extension system by creating a new
XWalkExtensionManager.

The backend implementation for XWalkExtension is abstracted as
XWalkExtensionBridge interface. Currently, one backend implementation
based on xwalk core is provided as default.

BUG=https://crosswalk-project.org/jira/browse/XWALK-148
[Android] Add content scheme support

The content scheme is for the Uris used by android content
provider. They are commonly used on android to retrieve
resources.

For detail information of android content provider, please referring
http://developer.android.com/guide/topics/providers/content-providers.html.

BUG=https://crosswalk-project.org/jira/browse/XWALK-165
TEST=org.xwalk.core.xwview.test.LoadUrlTest#testContentUrl
[Android] Add extension JS files to runtime client embedded shell

Fixes bug that runtime client embedded shell can not find Javascript
stubs of runtime internal extensions.

BUG=https://crosswalk-project.org/jira/browse/XWALK-126
Merge pull request #1074 from hmin/extension-refactor

[Android] Refactor Java extension system
Merge pull request #1088 from wang16/content_scheme

[Android] Add content scheme support
Merge pull request #1103 from DonnaWuDongxia/embed

[Android] Add extension JS files to runtime client embedded shell
[Android] Enable Web Audio on x86 -- part 1

Openmax_dl has contained the x86 implementation which is needed to
enable the Web Audio feature on IA. We want to enable it right now
so we update the deps with changing openmax_dl to the version
contains the x86 fft support directly.

*Attention when rebasing!*
The patch should be removed as long as the chromium has updated the
dependence of openmax_dl to r5113 or higher versions.