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>

BUG=chromium:652188
TBR=fbarchard@chromium.org

Review URL: https://codereview.chromium.org/2427643003 .

BUG=chromium:652188
TBR=ehmaldonado@chromium.org

Review URL: https://codereview.chromium.org/2421343002 .

After switching bots from GYP to GN, build artifacts are left that fails
the next builds. Since it's unfeasible to clean out all bot machines
it's better to have an automated system for this, which is what landmines is.

By adding a line to tools/get_landmines.py it is possible to clobber each bot
that syncs past that "landmine CL".

BUG=chromium:652188
TBR=ehmaldonado@chromium.org

Review URL: https://codereview.chromium.org/2427633003 .