[Android] Implement runtime client with runtime library embedded

We should support both sharing and embeding mode for runtime
client to use runtime library, which providing java class, native
lib and pak resources for runtime client.

Currently, only sharing mode is implemented. In sharing mode,
runtime library is an Android app.

This commit implements an alternative to allow packing runtime lib
embedded in runtime client. The api will stay unchanged and the
client of runtimeView will not aware the difference.

Add a new target, xwalk_runtime_client_embedded_shell, which is
the shell using runtime view with library embeded. It's for
testing purpose.

TODO=https://github.com/crosswalk-project/crosswalk/issues/657
BUG=https://github.com/crosswalk-project/crosswalk/issues/640