Enable -Winconsistent-missing-override flag.

webrtc/build/common.gypi

 # Copyright (c) 2012 The WebRTC project authors. All Rights Reserved.
 #
 # Use of this source code is governed by a BSD-style license
 # that can be found in the LICENSE file in the root of the source
 # tree. An additional intellectual property rights grant can be found
 # in the file PATENTS.  All contributing project authors may
 # be found in the AUTHORS file in the root of the source tree.
 
 # This file contains common settings for building WebRTC components.
 
@@ skipping 291 matching lines @@
             'cflags_cc': [
               '-Wnon-virtual-dtor',
               # This is enabled for clang; enable for gcc as well.
               '-Woverloaded-virtual',
             ],
           }],
           ['clang==1', {
             'cflags': [
               '-Wimplicit-fallthrough',
               '-Wthread-safety',
+              '-Winconsistent-missing-override',
             ],
           }],
         ],
       }],
       ['target_arch=="arm64"', {
         'defines': [
           'WEBRTC_ARCH_ARM64',
           'WEBRTC_HAS_NEON',
         ],
       }],
@@ skipping 176 matching lines @@
           # For access to standard POSIXish features, use WEBRTC_POSIX instead
           # of a more specific macro.
           'defines': [
             'WEBRTC_POSIX',
           ],
         }],
       ],
     },
   }, # target_defaults
 }