This is the V8 equivalent to https://crrev.com/2779193002 and must be landed
before //build/secondary/{gtest,gmock} are removed from Chromium. This started
out as https://crrev.com/2847693002

The changes in tools/ were authored by yangguo@chromium.org and
initially shared in http://crrev.com/2849783003.

GoogleTest (gtest) and GoogleMock (gmock) are now hosted into the same
googletest repository. In order to cope with this, the googletest
repository is now sourced at third_party/googletest.

The file/directory layout of Google Test is not yet considered stable.
To minimize disruption while Google Test stabilizes, Chromium code will
be insulated from third_party/googletest.

* testing/gtest/include/gtest/ and testing/gmock/include/gmock have
  been populated with headers that forward into the appropriate
  locations of third_party/googletest

* testing/BUILD.gn has been populated with the targets
  //testing/gtest(:gtest_main) and //testing/gmock(:gmock_main),
  which depend on the appropriate //third_party/googletest targets.

All Chromium code should keep depending on the targets and
headers in testing/{gtest,gmock} for now.

BUG=chromium:630705

Change-Id: I12b07ae78c8039aeff6ada7a3335e4e2b5d308ab
Reviewed-on: https://chromium-review.googlesource.com/639953Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Victor Costan <pwnall@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52170}