Enable "unreachable code" warning for MSVC.

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 4898 matching lines @@
                     'AdditionalLibraryDirectories':
                       ['<(windows_driver_kit_path)/lib/ATL/amd64'],
                   },
                   'VCLinkerTool': {
                     'AdditionalLibraryDirectories':
                       ['<(windows_driver_kit_path)/lib/ATL/amd64'],
                   },
                 },
               },
             },
+            # Warning 4702 should be re-enabled once Express users are updated
+            # to VS2013 Update 2.

[scottmg, 2014/05/22 23:39:06]

Please add crbug/what 4702 is here.

[Peter Kasting, 2014/05/23 17:51:16]

Done.

+            'msvs_disabled_warnings': [
+              4702
+            ],
             'msvs_settings': {
               'VCLinkerTool': {
                 # Explicitly required when using the ATL with express
                 'AdditionalDependencies': ['atlthunk.lib'],
 
                 # ATL 8.0 included in WDK 7.1 makes the linker to generate
                 # almost eight hundred LNK4254 and LNK4078 warnings:
                 #   - warning LNK4254: section 'ATL' (50000040) merged into
                 #     '.rdata' (40000040) with different attributes
                 #   - warning LNK4078: multiple 'ATL' sections found with
                 #     different attributes
                 'AdditionalOptions': ['/ignore:4254', '/ignore:4078'],
               },
             },
             'msvs_system_include_dirs': [
               '<(windows_driver_kit_path)/inc/atl71',
               '<(windows_driver_kit_path)/inc/mfc42',
             ],
           }],
         ],
         'msvs_system_include_dirs': [
           '<(windows_sdk_path)/Include/shared',
           '<(windows_sdk_path)/Include/um',
           '<(windows_sdk_path)/Include/winrt',
           '$(VSInstallDir)/VC/atlmfc/include',
         ],
         'msvs_cygwin_shell': 0,
-        'msvs_disabled_warnings': [4351, 4355, 4396, 4503, 4819,
+        'msvs_disabled_warnings': [
+          4351, 4355, 4396, 4503, 4819,
           # TODO(maruel): These warnings are level 4. They will be slowly
           # removed as code is fixed.
           4100, 4121, 4125, 4127, 4130, 4131, 4189, 4201, 4238, 4244, 4245,
-          4310, 4428, 4481, 4505, 4510, 4512, 4530, 4610, 4611, 4701, 4702,
-          4706,
+          4310, 4428, 4481, 4505, 4510, 4512, 4530, 4610, 4611, 4701, 4706,
         ],
         'msvs_settings': {
           'VCCLCompilerTool': {
             'AdditionalOptions': ['/MP'],
             'MinimalRebuild': 'false',
             'BufferSecurityCheck': 'true',
             'EnableFunctionLevelLinking': 'true',
             'RuntimeTypeInfo': 'false',
             'WarningLevel': '4',
             'WarnAsError': 'true',
@@ skipping 359 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',
   },
 }