win: Stop disabling compiler warning 4481.

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")
 import("//build/config/compiler/compiler.gni")
 import("//build/config/nacl/config.gni")
 import("//build/toolchain/ccache.gni")
 
@@ skipping 714 matching lines @@
       # use setjmp/longjmp for e.g. JPEG decode error handling, which means we
       # have to turn off this warning (and be careful about how object
       # destruction happens in such cases).
       "/wd4611",
 
       # Warnings to evaluate and possibly fix/reenable later:
 
       "/wd4100",  # Unreferenced formal function parameter.
       "/wd4121",  # Alignment of a member was sensitive to packing.
       "/wd4244",  # Conversion: possible loss of data.
-      "/wd4481",  # Nonstandard extension: override specifier.
       "/wd4505",  # Unreferenced local function has been removed.
       "/wd4510",  # Default constructor could not be generated.
       "/wd4512",  # Assignment operator could not be generated.
       "/wd4610",  # Class can never be instantiated, constructor required.
       "/wd4838",  # Narrowing conversion. Doesn't seem to be very useful.
       "/wd4995",  # 'X': name was marked as #pragma deprecated
       "/wd4996",  # Deprecated function warning.
 
       # These are variable shadowing warnings that are new in VS2015. We
       # should work through these at some point -- they may be removed from
@@ skipping 562 matching lines @@
   if (symbol_level == 0) {
     configs = [ ":no_symbols" ]
   } else if (symbol_level == 1) {
     configs = [ ":minimal_symbols" ]
   } else if (symbol_level == 2) {
     configs = [ ":symbols" ]
   } else {
     assert(false)
   }
 }