clang/win: Enable -Wmicrosoft-unqualified-friend.

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 846 matching lines @@
     default_warning_flags += [ "/wd4702" ]  # Unreachable code.
   }
 
   # Building with Clang on Windows is a work in progress and very
   # experimental. See crbug.com/82385.
   # Keep this in sync with the similar block in build/common.gypi
   if (is_clang) {
     default_warning_flags += [
       # TODO(hans): Make this list shorter eventually, http://crbug.com/504657
       "-Qunused-arguments",  # http://crbug.com/504658
-      "-Wno-microsoft-unqualified-friend",  # http://crbug.com/505296
       "-Wno-microsoft-enum-value",  # http://crbug.com/505296
       "-Wno-unknown-pragmas",  # http://crbug.com/505314
       "-Wno-unused-value",  # http://crbug.com/505318
     ]
   }
 } else {
   # Common GCC warning setup.
   default_warning_flags += [
     # Enables.
     "-Wendif-labels",  # Weird old-style text after an #endif.
@@ skipping 460 matching lines @@
       cflags += [ "-gsplit-dwarf" ]
     }
   }
 }
 
 config("no_symbols") {
   if (!is_win) {
     cflags = [ "-g0" ]
   }
 }