build WebRTC for android

1. gclient config https://webrtc.googlecode.com/svn/trunk
2. add "target_os = ['android'] to .gclient (at the very end, outside all brackets)
3. gclient sync
4. cd trunk
5. source ./build/android/envsetup.sh
6. gclient runhooks
7. GYP_GENERATORS=ninja ./build/gyp_chromium --depth=. webrtc.gyp
8. ninja -C out/Debug All

9 . cd webrtc/video_engine/test/android/

10. ndk-build

11. ant debug install

[ 注] 最新代码已经不适用！参考官方http://www.webrtc.org/reference/getting-started即可！