clang/win: Enable -Woverloaded-virtual globally.

build/config/compiler/BUILD.gn

 # Copyright (c) 2013 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.
 
 import("//build/config/android/config.gni")
 import("//build/config/chrome_build.gni")
 if (current_cpu == "arm") {
   import("//build/config/arm.gni")
 }
 if (current_cpu == "mipsel" || current_cpu == "mips64el") {
@@ skipping 1031 matching lines @@
   if (is_linux) {
     # Don't warn about ignoring the return value from e.g. close(). This is
     # off by default in some gccs but on by default in others. BSD systems do
     # not support this option, since they are usually using gcc 4.2.1, which
     # does not have this flag yet.
     cflags += [ "-Wno-unused-result" ]
   }
 
   if (is_clang) {
     cflags += [
-      # TODO(mgiuca): Move this suppression into individual third-party
-      # libraries as required. http://crbug.com/505301.
-      "-Wno-overloaded-virtual",
-
       # TODO(thakis): Move this suppression into individual third-party
       # libraries as required. http://crbug.com/505316.
       "-Wno-unused-function",
 
       # Lots of third-party libraries have unused variables. Instead of
       # suppressing them individually, we just blanket suppress them here.
       "-Wno-unused-variable",
     ]
   }
 
@@ skipping 265 matching lines @@
       cflags += [ "-gsplit-dwarf" ]
     }
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }