clang/win: Build chromium_code with -Wunused-function

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 1db19c1b557bcd173941ef307c8b07df14a40870..6f24175aee79bd53fd418222077795241ec2a363 100644
--- a/build/config/compiler/BUILD.gn
+++ b/build/config/compiler/BUILD.gn
@@ -849,7 +849,6 @@ if (is_win) {
       "-Wno-microsoft",  # http://crbug.com/505296
       "-Wno-switch",  # http://crbug.com/505308
       "-Wno-unknown-pragmas",  # http://crbug.com/505314
-      "-Wno-unused-function",  # http://crbug.com/505316
       "-Wno-unused-value",  # http://crbug.com/505318
     ]
   }
@@ -1042,6 +1041,10 @@ config("no_chromium_code") {
       # 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",