Refactored SkColorSpace and added in a Lab PCS GM

include/core/SkColorSpace.h

 /*
  * Copyright 2016 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef SkColorSpace_DEFINED
 #define SkColorSpace_DEFINED
 
@@ skipping 48 matching lines @@
      */
     static sk_sp<SkColorSpace> NewNamed(Named);
 
     /**
      *  Create an SkColorSpace from an ICC profile.
      */
     static sk_sp<SkColorSpace> NewICC(const void*, size_t);
 
     /**
      *  Create an SkColorSpace with the same gamut as this color space, but with linear gamma.
+     *  If this is not possible due to the color space specification, nullptr is returned.

[msarett, 2016/10/11 13:40:30]

I'm still struggling with this...  Though I don't have the answer.

      */
     sk_sp<SkColorSpace> makeLinearGamma();
 
     /**
      *  Returns true if the color space gamma is near enough to be approximated as sRGB.
      */
     bool gammaCloseToSRGB() const;
 
     /**
      *  Returns true if the color space gamma is linear.
@@ skipping 18 matching lines @@
      *  If both are null, we return true.  If one is null and the other is not, we return false.
      *  If both are non-null, we do a deeper compare.
      */
     static bool Equals(const SkColorSpace* src, const SkColorSpace* dst);
 
 protected:
     SkColorSpace() {}
 };
 
 #endif