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

ui/views/cocoa/native_widget_mac_nswindow.mm

 // Copyright 2014 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.
 
 #import "ui/views/cocoa/native_widget_mac_nswindow.h"
 
 #include "base/mac/foundation_util.h"
+#import "ui/views/cocoa/cocoa_non_client_drag.h"
 #import "ui/views/cocoa/views_nswindow_delegate.h"
 #include "ui/views/controls/menu/menu_controller.h"
 #include "ui/views/widget/native_widget_mac.h"
 
 @interface NativeWidgetMacNSWindow ()
 - (ViewsNSWindowDelegate*)viewsNSWindowDelegate;
 - (views::Widget*)viewsWidget;
 - (BOOL)hasViewsMenuActive;
 @end
 
@@ skipping 82 matching lines @@
     return;
   }
 
   NSCursor* cursor = [[self viewsNSWindowDelegate] cursor];
   if (cursor)
     [cursor set];
   else
     [super cursorUpdate:theEvent];
 }
 
+// NativeWidgetMacNSWindow (CocoaNonClientDrag) implementation.
+
+- (BOOL)willReceiveLeftMouseDown:(NSPoint)locationInWindow {
+  return [[self viewsNSWindowDelegate]
+      onWindowWillReceiveLeftMouseDown:locationInWindow];
+}
+
 @end