The following are not yet available in their respective libraries so
attempts to use it in webrtc result in a call to abort():
* libvpx's CONSTRAINED_FROM_ABOVE_DROP constant
* libyuv's I010 buffers
The original webrtc project expects to have third party libraries
checked out in third_party/ and base/third_party/. Added some headers
in those libraries with a single line including the right header from
external/<library>. Updated .gitignore to keep track of said headers.
Bug: 153469641
Test: mm, also built cuttlefish using this library and ran it locally
Change-Id: I2d596942e34093dccc65d4b7b8249b6afc14d31f
