Fixed all unused-variable Clang warnings on Windows.

ui/aura/window_tree_host_win.cc

Index: ui/aura/window_tree_host_win.cc
diff --git a/ui/aura/window_tree_host_win.cc b/ui/aura/window_tree_host_win.cc
index 6f879ab1cad9cd283c51e6c2524213f5480c636c..810b5e1575f5d1ad02abe21ecb05f4e8fee16812 100644
--- a/ui/aura/window_tree_host_win.cc
+++ b/ui/aura/window_tree_host_win.cc
@@ -25,11 +25,6 @@ using std::max;
 using std::min;
 
 namespace aura {
-namespace {
-
-bool use_popup_as_root_window_for_test = false;
-
-}  // namespace
 
 // static
 WindowTreeHost* WindowTreeHost::Create(const gfx::Rect& bounds) {