Remove win_third_party_warn_as_error.

build/common.gypi

 # 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.
 
 # IMPORTANT:
 # Please don't directly include this file if you are building via gyp_chromium,
 # since gyp_chromium is automatically forcing its inclusion.
 {
   # Variables expected to be overriden on the GYP command line (-D) or by
   # ~/.gyp/include.gypi.
@@ skipping 1222 matching lines @@
     # to get incremental linking to be faster in debug builds.
     'incremental_chrome_dll%': '0',
 
     # Experimental setting to break chrome.dll into multiple pieces based on
     # process type.
     'chrome_multiple_dll%': '0',
 
     # Experimental setting to optimize Chrome's DLLs with PGO.
     'chrome_pgo_phase%': '0',
 
-    # The default settings for third party code for treating
-    # warnings-as-errors. Ideally, this would not be required, however there
-    # is some third party code that takes a long time to fix/roll. So, this
-    # flag allows us to have warnings as errors in general to prevent
-    # regressions in most modules, while working on the bits that are
-    # remaining.
-    'win_third_party_warn_as_error%': 'true',
-
     # Clang stuff.
     'clang%': '<(clang)',
     'make_clang_dir%': 'third_party/llvm-build/Release+Asserts',
 
     # Control which version of clang to use when building for iOS.  If set to
     # '1', uses the version of clang that ships with Xcode.  If set to '0', uses
     # the version of clang that ships with the Chromium source.  This variable
     # is automatically set to '1' when using the Xcode generator.
     'clang_xcode%': 0,
 
@@ skipping 1682 matching lines @@
             'defines': [
               '_CRT_SECURE_NO_DEPRECATE',
               '_CRT_NONSTDC_NO_WARNINGS',
               '_CRT_NONSTDC_NO_DEPRECATE',
               '_SCL_SECURE_NO_DEPRECATE',
             ],
             'msvs_disabled_warnings': [4800],
             'msvs_settings': {
               'VCCLCompilerTool': {
                 'WarningLevel': '3',
-                'WarnAsError': '<(win_third_party_warn_as_error)',
+                'WarnAsError': 'true',
                 'Detect64BitPortabilityProblems': 'false',
               },
             },
             'conditions': [
               ['buildtype=="Official"', {
                 'msvs_settings': {
                   'VCCLCompilerTool': { 'WarnAsError': 'false' },
                 }
               }],
               ['clang==1', {
@@ skipping 2691 matching lines @@
     # settings in target dicts.  SYMROOT is a special case, because many other
     # Xcode variables depend on it, including variables such as
     # PROJECT_DERIVED_FILE_DIR.  When a source group corresponding to something
     # like PROJECT_DERIVED_FILE_DIR is added to a project, in order for the
     # files to appear (when present) in the UI as actual files and not red
     # red "missing file" proxies, the correct path to PROJECT_DERIVED_FILE_DIR,
     # and therefore SYMROOT, needs to be set at the project level.
     'SYMROOT': '<(DEPTH)/xcodebuild',
   },
 }