Turn MoveLeave event sending into a feature for testing enabling it.

ui/events/blink/blink_features.cc

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "ui/events/blink/blink_features.h"
 
 namespace features {
 
 // Enables VSync aligned input for GestureScroll/Pinch on compositor thread.
 // Tracking: https://crbug.com/625689
 const base::Feature kVsyncAlignedInputEvents{"VsyncAlignedInput",
                                              base::FEATURE_DISABLED_BY_DEFAULT};
 
+const base::Feature kSendMouseLeaveEvents {
+  "SendMouseLeaveEvents",
+// TODO(chaopeng) this fix only for chromeos now, should convert ET_MOUSE_EXITED
+// to MouseLeave when crbug.com/450631 fixed.
+#if defined(OS_CHROMEOS)
+      base::FEATURE_ENABLED_BY_DEFAULT
+#else
+      base::FEATURE_DISABLED_BY_DEFAULT
+#endif
+};
 }