Should do color space mapping when upload DOM elemet to sRGB formated texture?

Current conformance test doesn't do color space mapping for such case. What do you think?
@kenrussell @zhenyao

Start by locating the conformance test covering uploads from a DOM element into an sRGB-formatted texture. Read the existing color-space expectations and the WebGL texture-upload path it exercises. Done means the test clearly establishes whether color space mapping is required and passes with the expected behavior.

Written by the indexing model from the issue text.