Already done for 2D canvas. You get this behaviour by default when color correct rendering is enabled.  OTherwise, you just have to create the context with:
var ctx = canvas.getContext('2d', {colorSpace: 'srgb'});

For webGL, The plumbing for color space support is all there already.  The only things missing are to make WebGLRenderingContextBase and friends take into account CanvasRenderingContext::skColorSpace to infer any necessary transforms that need to be applied on texture uploads, and to plumb the colorspace down to DrawingBuffer to get the compositing right.

The code changes are trivial. Most of the work will be in writing tests.

Actually, IIRC we discussed this, and we don't want to do any automatic colorspace transforms on texture uploads. The transforms are to be made explicit fore example, by using creatImageBitmap, is that right.  We need to put more though into how we are going to spec this for the texImage* methods.