Add structure packing support for mojo modules

BUG=None
TEST=new tests
R=viettrungluu@chromium.org, viettrungluu

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=230837

Review URL: https://codereview.chromium.org/27226006

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@230971 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 230971