[Android] Implement loading app from manifest file.

When the Java method AppFromManifest() in Java class XWalkView is
called, the manifest string will be passed to c++ side, it will be
parsed by the manifest parser. If a valid target URL could be got,
it will be passed back to the Java side, the Java class XWalkContent
will navigate to target page with the URL.

To comunicate between C++ and Java, the following interfaces are
added to XWalkContent.java:
1. The native method nativeSetManifest().
2. The Java method onGetUrlFromManifest() called by native.

BUG=#621
[Android] Add test case for loadAppFromManifest().

This patch contains the test case about loadAppFromManifest on
embedded and shared mode.
Invoke loadAppFromManifest on main thread, then get the title
and compare the two titles.

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

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 testLoadAppFromManifest
Merge pull request #972 from gaochun/load_app_from_manifiest

[Android] Implement loading app from manifest file.