MacViews: Fix window dragging on Sierra.

ui/views/cocoa/bridged_native_widget.h

Index: ui/views/cocoa/bridged_native_widget.h
diff --git a/ui/views/cocoa/bridged_native_widget.h b/ui/views/cocoa/bridged_native_widget.h
index 58c60b659c0d06de71a6efbe08a2270a04c6c6d0..4a4acdefa6298d22295e548523ac62516c25969e 100644
--- a/ui/views/cocoa/bridged_native_widget.h
+++ b/ui/views/cocoa/bridged_native_widget.h
@@ -67,6 +67,9 @@ class VIEWS_EXPORT BridgedNativeWidget
   static gfx::Size GetWindowSizeForClientSize(NSWindow* window,
                                               const gfx::Size& size);
 
+  // Whether an event monitor should be used to intercept window drag events.
+  static bool ShouldUseDragEventMonitor();
+
   // Creates one side of the bridge. |parent| must not be NULL.
   explicit BridgedNativeWidget(NativeWidgetMac* parent);
   ~BridgedNativeWidget() override;
@@ -151,11 +154,16 @@ class VIEWS_EXPORT BridgedNativeWidget
   // Called by the NSWindowDelegate when the window becomes or resigns key.
   void OnWindowKeyStatusChangedTo(bool is_key);
 
-  // Called by NSWindowDelegate when the application receives a mouse-down, but
-  // before the event is processed by NSWindows. Returning true here will cause
-  // the event to be cancelled and reposted at the CGSessionEventTap level. This
-  // is used to determine whether a mouse-down should drag the window.
-  virtual bool ShouldRepostPendingLeftMouseDown(NSPoint location_in_window);
+  // Returns true if the |event| should initiate a window drag.
+  bool ShouldDragWindow(NSEvent* event);
+
+  // Called when the application receives a mouse-down, but before the event is
+  // processed by NSWindow. Returning true here will cause the event to be
+  // cancelled and reposted at the CGSessionEventTap level. This is used to
+  // determine whether a mouse-down should drag the window. Only called when
+  // ShouldUseDragEventMonitor() returns true.
+  // Virtual for testing.
+  virtual bool ShouldRepostPendingLeftMouseDown(NSEvent* event);
 
   // Called by NativeWidgetMac when the window size constraints change.
   void OnSizeConstraintsChanged();