Added ACM_dump protobuf, class for reading/writing and unittest.

This adds a class to read and write ACM_dump protobuf files. In this CL
it is not hooked up to actually store any packets or debug events.
The unittest writes two dummy RTP packets to disk and reads them to see
if they contain the expected data.

BUG=webrtc:4741
R=andrew@webrtc.org, henrik.lundin@webrtc.org, kjellander@webrtc.org, kwiberg@webrtc.org, tina.legrand@webrtc.org

Review URL: https://webrtc-codereview.appspot.com/52059005

Cr-Commit-Position: refs/heads/master@{#9460}

DEPS

@@ -34,6 +34,7 @@ include_rules = [
   # WebRTC production code.
   '-base',
   '-chromium',
+  '+external/webrtc/webrtc',  # Android platform build.
   '+gflags',
   '+libyuv',
   '+net',