Add methods for hashing pairs of integer values.

cc/cc.gyp

 # Copyright (c) 2012 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.
 
 {
   'variables': {
     'chromium_code': 0,
     'use_libcc_for_compositor%': 0,
     'cc_source_files': [
+      'hash_pair.h',
       'BitmapCanvasLayerTextureUpdater.cpp',
       'BitmapCanvasLayerTextureUpdater.h',
       'BitmapSkPictureCanvasLayerTextureUpdater.cpp',
       'BitmapSkPictureCanvasLayerTextureUpdater.h',
       'CCActiveAnimation.cpp',
       'CCActiveAnimation.h',
       'CCAppendQuadsData.h',
       'CCAnimationCurve.cpp',
       'CCAnimationCurve.h',
       'CCAnimationEvents.h',
@@ skipping 243 matching lines @@
             'stubs/SkiaUtils.h',
             'stubs/TilingData.h',
             'stubs/TraceEvent.h',
             'stubs/UnitBezier.h',
           ],
         }],
       ],
     },
   ],
 }