[Android] Support xwalk_host member for manifest.json

The xwalk_host member allow application developer to add URL
match patterns as white list for allow Cross-Origin access.

BUG=https://crosswalk-project.org/jira/browse/XWALK-1353
[Android] Add tests for Cross-Origin XHR.

For embedded client test:
1. install XWalkRuntimeClientEmbeddedShell.apk
2. python build/android/test_runner.py instrumentation \
--test-apk=XWalkRuntimeClientEmbeddedTest -v -f \
testCrossOriginXhr

For shared client test:
1. install XWalkRuntimeLib.apk
2. install XWalkRuntimeClientShell.apk
3. python build/android/test_runner.py instrumentation \
--test-apk=XWalkRuntimeClientTest -v -f testCrossOriginXhr