[Android] Add test case for onJavascriptCloseWindow().

This patch is to add test case about onJavascriptCloseWindow().
Load a html, it will call "window.close()", then
onJavascriptCloseWindow() will be called. The called flag will be
marked with the help of TestHelperBridge. Get this flag and compare
it with the expected result.
[Android] Enable instrument test for Messaging API.

Enable instrument test for Messaging API.
[Android] Support 'xwalk_description' field in manifest.

Support 'xwalk_description' field in manifest according to W3C manifest spec.
The legacy field 'description' are still supported, but will print a warning message.
Merge pull request #2226 from jinbang/tool_support_manifest_xwalk_description

[Android] Support 'xwalk_description' field in manifest.
Merge pull request #2239 from shawngao5/enable_messaging_test

[Android] Enable instrument test for Messaging API.
Merge pull request #1995 from wuhengzhi/onJavascriptCloseWindow_test

[Android] Add test case for onJavascriptCloseWindow().
[Android] Add samples for XWalkUIClient.

This patch is to add samples for the interfaces in XWalkUIClient.java.
The feature about "onScaleChanged" does not work since the bridge code
was not implemented.