clang/win: Build chromium_code with -Wunused-function

build/common.gypi

Index: build/common.gypi
diff --git a/build/common.gypi b/build/common.gypi
index 70ea06c41abc2b287b9c38a23c65e3186e27e3ef..586dc2140567d0b3fa078d00d1f9cce2cebd0dde 100644
--- a/build/common.gypi
+++ b/build/common.gypi
@@ -3148,6 +3148,9 @@
             # 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',
             # Lots of third-party libraries have unused variables. Instead of
             # suppressing them individually, we just blanket suppress them here.
             '-Wno-unused-variable',
@@ -5803,7 +5806,6 @@
                   '-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
                 ],
               },