Re-add PassRefPtr constructors erroneously removed in r154312

Raw pointers passed to WebGLGetInfo are coerced to bools instead of PassRefPtrs,
thus the need to explicitly construct PassRefPtrs.

TBR=esprehn

Review URL: https://codereview.chromium.org/19371003

git-svn-id: svn://svn.chromium.org/blink/trunk@154315 bbb929c8-8fbe-4397-9dbb-9b2b20218538