Add SkColorSpace::Equals() API

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 86 matching lines @@
     sk_sp<SkData> serialize() const;
 
     /**
      *  If |memory| is nullptr, returns the size required to serialize.
      *  Otherwise, serializes into |memory| and returns the size.
      */
     size_t writeToMemory(void* memory) const;
 
     static sk_sp<SkColorSpace> Deserialize(const void* data, size_t length);
 
+    /**
+     *  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(GammaNamed gammaNamed, const SkMatrix44& toXYZD50, Named named);
 
     const GammaNamed fGammaNamed;
     const SkMatrix44 fToXYZD50;
     const Named      fNamed;
 };
 
 #endif