Removed -Wno-overloaded-virtual warning suppression.

build/config/compiler/BUILD.gn

Index: build/config/compiler/BUILD.gn
diff --git a/build/config/compiler/BUILD.gn b/build/config/compiler/BUILD.gn
index 56b79b560b4c67e730e1bcbc5db6519626b633b4..c1061af307e4b03112c72a6f9e9eeadeab131017 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -806,7 +806,6 @@ if (is_win) {
       "-Wno-microsoft",  # http://crbug.com/505296
       "-Wno-missing-braces",  # http://crbug.com/505297
       "-Wno-msvc-include",  # http://crbug.com/505299
-      "-Wno-overloaded-virtual",  # http://crbug.com/505301
       "-Wno-pointer-sign",  # http://crbug.com/505303
       "-Wno-reorder",  # http://crbug.com/505304
       "-Wno-switch",  # http://crbug.com/505308
@@ -995,6 +994,14 @@ config("no_chromium_code") {
     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",
+    ]
+  }
+
   if (is_linux || is_android) {
     cflags += [
       # Don't warn about printf format problems. This is off by default in gcc