"Add callback support for stdout and stderr."
"Add tests for both universal_newlines=True and False."
"Implement accelerated tee support for POSIX."

The reason is that the semantic of
subprocess2.check_call(cmd, timeout=60, stderr=subprocess2.STDOUT) changed,
stderr wasn't redirected to VOID anymore and for an unknown reason, it was
hanging until the timeout happened. Will reapply r109239 with a new regression
test to detect that bug.

TBR=dpranke@chromium.org
BUG=
TEST=


Review URL: http://codereview.chromium.org/8505046

git-svn-id: svn://svn.chromium.org/chrome/trunk/tools/depot_tools@109369 0039d316-1c4b-4281-b951-d872f2087c98