Remove the --ui-enable-threaded-compositing flag.

ui/compositor/compositor.cc

Index: ui/compositor/compositor.cc
diff --git a/ui/compositor/compositor.cc b/ui/compositor/compositor.cc
index 7061599e8e9f742c959589c65613c7fc819b2182..d0e2d97b533ffcf9b5cdf3fe42b605e6fd370c6c 100644
--- a/ui/compositor/compositor.cc
+++ b/ui/compositor/compositor.cc
@@ -278,11 +278,7 @@ void Compositor::Initialize() {
   bool use_thread = !CommandLine::ForCurrentProcess()->HasSwitch(
       switches::kUIDisableThreadedCompositing);
 #else
-  bool use_thread =
-      CommandLine::ForCurrentProcess()->HasSwitch(
-          switches::kUIEnableThreadedCompositing) &&
-      !CommandLine::ForCurrentProcess()->HasSwitch(
-          switches::kUIDisableThreadedCompositing);
+  bool use_thread = false;
 #endif
   if (use_thread) {
     g_compositor_thread = new base::Thread("Browser Compositor");