Disable Warning 4702 for the PGO builds.

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 4949 matching lines @@
                       'VCCLCompilerTool': {
                         # 2, optimizeMaxSpeed, Maximize Speed (/O2)
                         'Optimization': '2',
                         # 1, favorSpeed - Favor fast code (/Ot)
                         'FavorSizeOrSpeed': '1',
                       },
                     },
                   },
                 ],
                 ['optimize=="max"', {
+                    # Disable Warning 4702 ("Unreachable code") for the WPO/PGO
+                    # builds. Probably anything that this would catch that
+                    # wouldn't be caught in a normal build isn't going to
+                    # actually be a bug, so the incremental value of C4702 for
+                    # PGO builds is likely very small.
+                    'msvs_disabled_warnings': [
+                      4702
+                    ],
                     'msvs_settings': {
                       'VCCLCompilerTool': {
                         # 2, optimizeMaxSpeed, Maximize Speed (/O2)
                         'Optimization': '2',
                         # 1, favorSpeed - Favor fast code (/Ot)
                         'FavorSizeOrSpeed': '1',
                         # This implies link time code generation.
                         'WholeProgramOptimization': 'true',
                       },
                     },
@@ skipping 449 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',
   },
 }