Make runtest.py pass --test-launcher-bot-mode flag to gtest executables.
Make runtest.py pass --test-launcher-bot-mode flag to gtest executables.

This is a relanding of https://codereview.chromium.org/72383006

BUG=236893

Review URL: https://codereview.chromium.org/109993004

git-svn-id: 239fca9b83025a0b6f823aeeca02ba5be3d9fd76@240231 0039d316-1c4b-4281-b951-d872f2087c98

eunchong/build,eunchong/build,eunchong/build,eunchong/build