Add TSan flags to download_build_install.py
Allows building with both tsan=1 and use_instrumented_libraries=1

BUG=313751
TBR=earthdok@chromium.org

Review URL: https://codereview.chromium.org/195763021

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@257086 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 257086