Add GrSet class built on top of RedBlackTree

src/gpu/GrRedBlackTree.h

 /*
  * Copyright 2011 Google Inc.
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 #ifndef GrRedBlackTree_DEFINED
 #define GrRedBlackTree_DEFINED
 
 #include "GrConfig.h"
 #include "SkTypes.h"
 
 template <typename T>
 class GrLess {
 public:
     bool operator()(const T& a, const T& b) const { return a < b; }
 };
 
 template <typename T>
 class GrLess<T*> {
 public:
     bool operator()(const T* a, const T* b) const { return *a < *b; }
 };
 
+class GrStrLess {
+public:
+    bool operator()(const char* a, const char* b) const { return strcmp(a,b) < 0; }
+};
+
 /**
  * In debug build this will cause full traversals of the tree when the validate
  * is called on insert and remove. Useful for debugging but very slow.
  */
 #define DEEP_VALIDATE 0
 
 /**
  * A sorted tree that uses the red-black tree algorithm. Allows duplicate
  * entries. Data is of type T and is compared using functor C. A single C object
  * will be created and used for all comparisons.
@@ skipping 898 matching lines @@
                     return validateChildRelationsFailed();
                 }
             }
         }
     }
     return true;
 }
 #endif
 
 #endif