Import TestRunner library into chromium.

The reasons for the move are:

- it's actually a blink embedder, so it can't use blink/wtf types
- it can't use base either
- we want to replace CppBoundClass with gin::Wrappable, not possible in blink

In the first step, this is mostly a 1:1 copy (except for include paths).
Follow-up CLs will move the test plugin and layout tests helpers and
clean up the coding style

BUG=324658
R=abarth@chromium.org, maruel@chromium.org, torne@chromium.org, jam@chromium.org
TBR=torne@chromium.org

Review URL: https://codereview.chromium.org/110533009

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@242095 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 242095