Gin: Add support for binding JS methods to C++ instance methods.

Also:
- Added support for computed properties to ObjectTemplateBuilder
- Realized it was possible for CreateFunctionTemplate to be just one template

BUG=
R=abarth@chromium.org, jyasskin@chromium.org

Review URL: https://codereview.chromium.org/103703002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@239126 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 239126