Fix color gamut xform matrices in GPU code

Now that we're not storing them transposed, we can plumb them to the
shader column-major all the way, and then multiply colors on the right, as
it should be.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2326093002

Review-Url: https://codereview.chromium.org/2326093002

src/gpu/GrColorSpaceXform.cpp

@@ -37,8 +37,7 @@ static inline bool matrix_is_almost_identity(const SkMatrix44& m,
 
 GrColorSpaceXform::GrColorSpaceXform(const SkMatrix44& srcToDst, SkAlphaType srcAlphaType)
     : fSrcAlphaType(srcAlphaType) {
-    // TODO: Fix this, and store things as column major!
-    srcToDst.asRowMajorf(fSrcToDst);
+    srcToDst.asColMajorf(fSrcToDst);
 }
 
 sk_sp<GrColorSpaceXform> GrColorSpaceXform::Make(SkColorSpace* src, SkColorSpace* dst,

src/gpu/glsl/GrGLSLShaderBuilder.cpp

@@ -149,7 +149,7 @@ void GrGLSLShaderBuilder::appendColorGamutXform(SkString* out,
                             "\tcolor.rgb = color.rgb / nonZeroAlpha;\n");
     }
     // Gamut xform, clamp to destination gamut
-    functionBody.append("\tcolor.rgb = clamp((vec4(color.rgb, 1.0) * xform).rgb, 0.0, 1.0);\n");
+    functionBody.append("\tcolor.rgb = clamp((xform * vec4(color.rgb, 1.0)).rgb, 0.0, 1.0);\n");
     if (kPremul_SkAlphaType == colorXformHelper->alphaType()) {
         // Re-multiply by alpha
         functionBody.append("\tcolor.rgb = color.rgb * nonZeroAlpha;\n");