Reland: Add some handle read/write helpers to mojo/common/test/test_utils.h

This helps to refactor raw_channel_posix_unittest to run on multiple
platforms.

TEST=mojo_common_unittests,mojo_system_unittests
BUG=None
TBR=viettrungluu@chromium.org

Review URL: https://codereview.chromium.org/176063002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252822 0039d316-1c4b-4281-b951-d872f2087c98
Blink roll 167633:167634

http://build.chromium.org/f/chromium/perf/dashboard/ui/changelog_blink.html?url=/trunk&range=167634:167634&mode=html
TBR=
BUG=

Review URL: https://codereview.chromium.org/175463003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252823 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252822
Update .DEPS.git

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252824 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 252824