mojo: add support for packing handles, arrays and pointers to structs

BUG=None
TEST=included
R=darin@chromium.org

Review URL: https://codereview.chromium.org/45443002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@231112 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 231112