Mojo: SimilarityTraits

Make it possible for users to extend the set of types that can be converted to or from a mojo::Array<T> (including mojo::String) or any generated struct.

Review URL: https://codereview.chromium.org/62333020

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237993 0039d316-1c4b-4281-b951-d872f2087c98
[Mojo] sample_app should draw a spinning cube

After this CL, sample_app draws a spinning cube. We're still driving the
animation off a timer rather than off vsync, but we're making progress. :)

Review URL: https://codereview.chromium.org/95653002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@237994 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 237994