clang/win: Enable -Woverloaded-virtual globally.

Previously, it was only enabled for chromium_code on Windows.

BUG=505301

Review URL: https://codereview.chromium.org/1296773002

Cr-Original-Commit-Position: refs/heads/master@{#343979}
Cr-Mirrored-From: https://chromium.googlesource.com/chromium/src
Cr-Mirrored-Commit: 6e4734b82f3fa0ed8fea5365ac92dde7e4c29a4f

common.gypi

@@ -3143,9 +3143,6 @@
       ['chromium_code==0', {
         'variables': {
           'clang_warning_flags': [
-            # 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',

config/compiler/BUILD.gn

@@ -1049,10 +1049,6 @@ config("no_chromium_code") {
 
   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",