Implement ARDrone video extension

This extension will accept the P264 stream, parse each packet into H264
file, then mux it into mp4. Then notify JS part to update a video
element src. On the web front, it use requestAnimationFrame and a
canvas element to reduce slpash issue.

So far the FPS is ~10fps with some status:
1. At the first 10 seconds, the screen will splash, get better after 10s,
  almost no splash after 15s.
2. Some times core dump when mux

Command to build:
===========
gyp --depth=. all.gyp && \
ninja -C out/Default/ && make_apk.py \
--package=org.xwalk.extensions.ardrone \
--extensions="./out/Default/gen/ardrone_video/" --arch=x86 \
--manifest="./examples/ardrone_video/manifest.json" && \
adb install -r Ardrone_0.0.0.1_x86.apk
Merge pull request #18 from halton/ardrone_video

Ardrone video support