This changes libyuv to use the DEPS file for pulling
down all dependencies (thus no Chromium checkout is needed any more).

Add tools_libyuv directory to contain libyuv-specific tools
(needed to avoid name collision with the now DEPSed tools/ directory
of Chromium, which is needed by the toolchain).
Add tools_libyuv/autoroller/roll_deps.py script to automatically
roll all entries in the DEPS file (copied from WebRTC).

third_party/ is now DEPSed as well, including the gtest configuration
headers that used to live inside the libyuv repo.

Add PRESUBMIT.py with a few simple checks + execution of PyLint and
Python unit tests. For PyLint a pylintrc file was also added.

Valgrind in tools_libyuv/valgrind was updated to make PRESUBMIT.py pass
and remove old tsan suppressions (not used).

Removed util/android/test_runner.py since it's no longer needed.

Buildbot changes in https://chromium-review.googlesource.com/436464 
are needed for the Memcheck bot to go green.

BUG=libyuv:676
NOTRY=True

Change-Id: Ib86fea2905a1656bba2933703ce5a59d29d8db6b
Reviewed-on: https://chromium-review.googlesource.com/436264
Commit-Queue: Henrik Kjellander <kjellander@chromium.org>
Reviewed-by: Frank Barchard <fbarchard@google.com>