Set up some of the webgl native functions as leaf calls

Set up some of the webgl native functions as leaf calls
(Note: We need a better way of doing this, maybe some way of specifying
this in the IDL itself)

The webgl bindings benchmark score goes up from 363 to 473

R=rmacnak@google.com

Committed: https://code.google.com/p/dart/source/detail?r=35717

[rmacnak, 2014-05-02 23:06:36]

I wonder if a heuristic like marking all the bindings as leafs unless they take
a function (or unknown type) parameter would do well.

[rmacnak, 2014-05-02 23:07:03]

lgtm

[siva, 2014-05-02 23:17:28]

Committed patchset #1 manually as r35717 (presubmit successful).