Extract pair hash functions so that they can be re-used outside of hash tables

cc/quads/render_pass.h

 // Copyright 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CC_QUADS_RENDER_PASS_H_
 #define CC_QUADS_RENDER_PASS_H_
 
 #include <utility>
 
 #include "base/basictypes.h"
@@ skipping 99 matching lines @@
   RenderPass();
 
  private:
   DISALLOW_COPY_AND_ASSIGN(RenderPass);
 };
 
 }  // namespace cc
 
 namespace BASE_HASH_NAMESPACE {
 #if defined(COMPILER_MSVC)
-template<>
-inline size_t hash_value<cc::RenderPass::Id>(const cc::RenderPass::Id& key) {
-  return hash_value<std::pair<int, int> >(
-      std::pair<int, int>(key.layer_id, key.index));
+inline size_t hash_value(const cc::RenderPass::Id& key) {
+  return base::HashPair(key.layer_id, key.index);
 }
 #elif defined(COMPILER_GCC)
 template<>
 struct hash<cc::RenderPass::Id> {
   size_t operator()(cc::RenderPass::Id key) const {
-    return hash<std::pair<int, int> >()(
-        std::pair<int, int>(key.layer_id, key.index));
+    return base::HashPair(key.layer_id, key.index);
   }
 };
 #else
 #error define a hash function for your compiler
 #endif  // COMPILER
 }  // namespace BASE_HASH_NAMESPACE
 
 namespace cc {
 typedef ScopedPtrVector<RenderPass> RenderPassList;
 typedef base::hash_map<RenderPass::Id, RenderPass*> RenderPassIdHashMap;
 }  // namespace cc
 
 #endif  // CC_QUADS_RENDER_PASS_H_