Android: patch adb to get screenshot

In system/core/adb, you can find the adb source. framebuffer_service.c shows the way to communicate with adbd.

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After recompile your adb, use following command:
$ ./adb framebuffer 2>&1 | tee > screen.rgb
You now get a raw rgb image. Further convert it to png:

$ ffmpeg -pix_fmt rgb565 -s 480x800 -f rawvideo -i screen.rgb -f image2 -y test.png