color: Always use parametric color spaces for raster

ui/gfx/color_space.h

Index: ui/gfx/color_space.h
diff --git a/ui/gfx/color_space.h b/ui/gfx/color_space.h
index f472af359fdf011060b221774dd763a8b6beed50..a7edf0ab578f9273f6f393333744a3f88cbc7d6c 100644
--- a/ui/gfx/color_space.h
+++ b/ui/gfx/color_space.h
@@ -42,6 +42,7 @@ class GFX_EXPORT ColorSpace {
     SMPTEST432_1,
     XYZ_D50,
     ADOBE_RGB,
+    ICC_PROFILE_REQUIRED,

[hubbe, 2017/03/13 17:59:09]

Why?

[ccameron, 2017/03/13 20:34:18]

In the CL description, I wrote
This enum denotes "the ICC profile is required to accurately represent this
color space".

Is there a more specific question here? It's hard for me to know what this
means.

[hubbe, 2017/03/13 20:38:56]

I don't understand why we don't use CUSTOM with the best possible approximation
here?

If there is a good explanation for that, I think it should be in the code, not
the CL description.

[ccameron, 2017/03/14 10:19:54]

Because we need to distinguish between when CUSTOM is accurately representing
the ICCProfile from which it came, and when it isn't. In particular:

1. For rasterization, it is necessary to use the parametric color space. We need
to know if this matches or does not match the display's true color space. Hence
why we need one space to be the approximation (used by raster) and one to be
precise (used by display).

2. For creating ColorTransforms this creates a simpler way of knowing if we can
use parametric-transform-in-a-shader that we've proven to be more efficient, or
if we must fall back to a LUT.
I've added more comments to the enums. Please also see the comments in
ICCProfile::GetParametricColorSpace and ICCProfile::GetColorSpace.

     CUSTOM,
     LAST = CUSTOM
   };
@@ -74,6 +75,7 @@ class GFX_EXPORT ColorSpace {
     IEC61966_2_1_HDR,
     // The same as LINEAR but is defined for all real values.
     LINEAR_HDR,
+    ICC_PROFILE_REQUIRED,

[hubbe, 2017/03/13 17:59:09]

Why?

     CUSTOM,
     LAST = CUSTOM,
   };