[MacViews] Enable dragging a window by its caption/draggable areas.

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 a4e4b1d9541b779f703730e6f5d15936e02527ab..5f52831ecbbff6776393bc61fb7753c8dc3b1c1d 100644
--- a/ui/views/cocoa/bridged_native_widget.h
+++ b/ui/views/cocoa/bridged_native_widget.h
@@ -132,6 +132,12 @@ class VIEWS_EXPORT BridgedNativeWidget : public ui::LayerDelegate,
   // 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);
+
   // Called by NativeWidgetMac when the window size constraints change.
   void OnSizeConstraintsChanged();
 
@@ -191,6 +197,10 @@ class VIEWS_EXPORT BridgedNativeWidget : public ui::LayerDelegate,
   // scale factor.
   void UpdateLayerProperties();
 
+  // Sets mouseDownCanMoveWindow on |bridged_view_| and triggers the NSWindow to
+  // update its draggable region.
+  void SetDraggable(bool draggable);
+
   // Overridden from CocoaMouseCaptureDelegate:
   void PostCapturedEvent(NSEvent* event) override;
   void OnMouseCaptureLost() override;