MacViews: Emit NOTIMPLEMENTED() in NativeWidgetMac::ViewRemoved() only when potentially dragging

ui/views/widget/native_widget_mac.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.
 
 #include "ui/views/widget/native_widget_mac.h"
 
 #import <Cocoa/Cocoa.h>
 
 #include "base/mac/foundation_util.h"
 #include "base/mac/scoped_nsobject.h"
@@ skipping 176 matching lines @@
 const ui::Layer* NativeWidgetMac::GetLayer() const {
   return bridge_ ? bridge_->layer() : nullptr;
 }
 
 void NativeWidgetMac::ReorderNativeViews() {
   if (bridge_)
     bridge_->SetRootView(GetWidget()->GetRootView());
 }
 
 void NativeWidgetMac::ViewRemoved(View* view) {
-  NOTIMPLEMENTED();
+  // TODO(tapted): Something for drag and drop might be needed here in future.
+  // See http://crbug.com/464581. A NOTIMPLEMENTED() here makes a lot of spam,
+  // so only emit it when a drag and drop could be likely.
+  if (IsMouseButtonDown())
+    NOTIMPLEMENTED();
 }
 
 void NativeWidgetMac::SetNativeWindowProperty(const char* name, void* value) {
   if (bridge_)
     bridge_->SetNativeWindowProperty(name, value);
 }
 
 void* NativeWidgetMac::GetNativeWindowProperty(const char* name) const {
   if (bridge_)
     return bridge_->GetNativeWindowProperty(name);
@@ skipping 506 matching lines @@
   [[ViewsNSWindowCloseAnimator alloc] initWithWindow:window];
 }
 
 - (void)animationDidEnd:(NSAnimation*)animation {
   [window_ close];
   [animation_ setDelegate:nil];
   [self release];
 }
 
 @end