Print Preview: Display a throbber when the user requests the system print

chrome/browser/printing/print_view_manager_observer.h

+// Copyright (c) 2011 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.
+
+#ifndef CHROME_BROWSER_PRINTING_PRINT_VIEW_MANAGER_OBSERVER_H_
+#define CHROME_BROWSER_PRINTING_PRINT_VIEW_MANAGER_OBSERVER_H_
+#pragma once
+
+namespace printing {
+
+// An interface the PrintViewManager uses to notify an observer when the print
+// dialog is shown. Register the observer via PrintViewManager::set_observer.
+class PrintViewManagerObserver {
+ public:
+  // Notifies the observer that the print dialog was shown.
+  virtual void OnPrintDialogShown() = 0;
+
+ protected:
+  virtual ~PrintViewManagerObserver() {}
+};
+
+}  // namespace printing
+
+#endif  // CHROME_BROWSER_PRINTING_PRINT_VIEW_MANAGER_OBSERVER_H_