Mojo: Test data pipes from the CoreImpl level.

Test basic data pipe functionality and also passing data pipe consumer
and producer handles over data pipes.

From here, confidence that data pipes mostly work (modulo known bugs,
and also some unknown) is much higher.

R=sky@chromium.org

Review URL: https://codereview.chromium.org/118693003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@241713 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 241713