Work around the crash in GYP's ninja generator on Windows.

tools/gyp/configurations.gypi

 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 {
   'variables': {
     'common_gcc_warning_flags': [
       '-Wall',
       '-Wextra', # Also known as -W.
       '-Wno-unused-parameter',
@@ skipping 350 matching lines @@
 
       # These targets assume that target_arch is passed in explicitly
       # by the containing project (e.g., chromium).
       'Debug': {
         'inherit_from': ['Debug<(chrome_target_os)<(dart_target_arch)']
       },
 
       'Release': {
         'inherit_from': ['Release<(chrome_target_os)<(dart_target_arch)']
       },
+
+      'conditions': [
+        # On Windows ninja generator has hardcorded configuration naming
+        # patterns and it expects that x64 configurations are named smth_x64.
+        # This is a workaround for the crash that these expectations cause.
+        [ 'OS=="win" and GENERATOR=="ninja"', {
+          'DebugX64_x64': {
+            'inherit_from': [ 'DebugX64' ]
+          },
+
+          'ReleaseX64_x64': {
+            'inherit_from': [ 'ReleaseX64' ]
+          },
+        }],
+      ],
     },
   },
 }