Adding x64 configurations for windows....

build/common.gypi

 # Copyright (c) 2009 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   'variables': {
     # .gyp files should set chromium_code to 1 if they build Chromium-specific
@@ skipping 424 matching lines @@
               'VCLinkerTool': {
                 'EnableCOMDATFolding': '1',
                 'LinkIncremental': '1',
               },
             },
           },
           'Release - no tcmalloc': {
             'inherit_from': ['Release'],
             'defines': ['NO_TCMALLOC'],
           },
+          'Debug_x64': {
+            'inherit_from': ['Debug'],
+            'msvs_configuration_platform': 'x64',
+          },
+          'Release_x64': {
+            'inherit_from': ['Release'],
+            'msvs_configuration_platform': 'x64',
+          },
+          'Purify_x64': {
+            'inherit_from': ['Purify'],
+            'msvs_configuration_platform': 'x64',
+          },
+          'Release - no tcmalloc_x64': {
+            'inherit_from': ['Release - no tcmalloc'],
+            'msvs_configuration_platform': 'x64',
+          },
         }],
       ],
     },
   },
   'conditions': [
     ['OS=="linux"', {
       'target_defaults': {
         # Enable -Werror by default, but put it in a variable so it can
         # be disabled in ~/.gyp/include.gypi on the valgrind builders.
         'variables': {
@@ skipping 449 matching lines @@
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }
 
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