Copy Valgrind scripts that was deleted from Chromium's tools/ to fix the Memcheck bot:
    valgrind/chrome_tests.bat
    valgrind/chrome_tests.py
    valgrind/chrome_tests.sh
    valgrind/common.py
    valgrind/gdb_helper.py
    valgrind/locate_valgrind.sh
    valgrind/memcheck_analyze.py
    valgrind/valgrind.gni
    valgrind/valgrind.sh
    valgrind/valgrind_test.py

valgrind_test.py was stripped of its Mac and Dr Memory specific parts, which
we don't use. There's still more cleanup to do, tracked in bugs.webrc.org/7849.

This is similar to changes in https://codereview.webrtc.org/2945753002.

BUG=libyuv:714
NOTRY=True

Change-Id: Ia6ba9bd3d3fca6f2ebe0e4f30e1eb39bb1a66813
Reviewed-on: https://chromium-review.googlesource.com/615162Reviewed-by: Henrik Kjellander <kjellander@chromium.org>
Commit-Queue: Henrik Kjellander <kjellander@chromium.org>