Move android_webview_build variable to toolchain.gypi to fix arm builders.

build/toolchain.gypi

 # Copyright 2013 the V8 project authors. All rights reserved.
 # Redistribution and use in source and binary forms, with or without
 # modification, are permitted provided that the following conditions are
 # met:
 #
 #     * Redistributions of source code must retain the above copyright
 #       notice, this list of conditions and the following disclaimer.
 #     * Redistributions in binary form must reproduce the above
 #       copyright notice, this list of conditions and the following
 #       disclaimer in the documentation and/or other materials provided
@@ skipping 64 matching lines @@
     # The setting is ignored if want_separate_host_toolset is 0.
     'v8_toolset_for_d8%': 'target',
 
     'host_os%': '<(OS)',
     'werror%': '-Werror',
     # For a shared library build, results in "libv8-<(soname_version).so".
     'soname_version%': '',
 
     # Allow to suppress the array bounds warning (default is no suppression).
     'wno_array_bounds%': '',
+
+    'variables': {
+      # This is set when building the Android WebView inside the Android build
+      # system, using the 'android' gyp backend.
+      'android_webview_build%': 0,
+    }
   },
   'conditions': [
     ['host_arch=="ia32" or host_arch=="x64" or clang==1', {
       'variables': {
         'host_cxx_is_biarch%': 1,
        },
      }, {
       'variables': {
         'host_cxx_is_biarch%': 0,
       },
@@ skipping 722 matching lines @@
                 'OptimizeReferences': '2',
                 'EnableCOMDATFolding': '2',
               },
             },
           }],  # OS=="win"
         ],  # conditions
       },  # Release
     },  # configurations
   },  # target_defaults
 }