[PATCH] [Android] Enhance the resource client

1 Define the error codes when resource loading failed, follow up
the defination of Android WebView.
http://developer.android.com/reference/android/webkit/WebViewClient.html

2 Enable the onLoadFinished(), by invoking the callback in onPageFinished().

BUG=XWALK-1562
Merge pull request #1855 from xingnan/resource-loading-refine

[Android] Enhance the resource client