[Android] Add adb_gdb_xwalk_runtime_client_embedded_shell for extension debugging

Xwalk extension is not attched to xwalk_core_shell, we needed to run xwalk_runtime_client_embedded_shell
to debug extension.
Merge pull request #1464 from yinli/adb_gdb_embedded_client

[Android] Add adb_gdb_xwalk_runtime_client_embedded_shell for extension ...