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
[email protected]

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

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@252822 0039d316-1c4b-4281-b951-d872f2087c98
diff --git a/mojo/mojo.gyp b/mojo/mojo.gyp
index 4c9a5fce..82cd8ab 100644
--- a/mojo/mojo.gyp
+++ b/mojo/mojo.gyp
@@ -259,6 +259,9 @@
       'sources': [
         'common/test/multiprocess_test_base.cc',
         'common/test/multiprocess_test_base.h',
+        'common/test/test_utils.h',
+        'common/test/test_utils_posix.cc',
+        'common/test/test_utils_win.cc',
       ],
     },
     {