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

chrome/browser/ui/webui/print_preview_handler.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_UI_WEBUI_PRINT_PREVIEW_HANDLER_H_
 #define CHROME_BROWSER_UI_WEBUI_PRINT_PREVIEW_HANDLER_H_
 #pragma once
 
 #include "base/memory/ref_counted.h"
 #include "base/memory/weak_ptr.h"
+#include "chrome/browser/printing/print_view_manager_observer.h"
 #include "chrome/browser/ui/shell_dialogs.h"
 #include "content/browser/webui/web_ui.h"
 
 class FilePath;
 class FundamentalValue;
 class PrintSystemTaskProxy;
 class StringValue;
 
 namespace printing {
 class PrintBackend;
 }
 
-// The handler for Javascript messages related to the "print preview" dialog.
+// The handler for Javascript messages related to the print preview dialog.
 class PrintPreviewHandler : public WebUIMessageHandler,
                             public base::SupportsWeakPtr<PrintPreviewHandler>,
-                            public SelectFileDialog::Listener {
+                            public SelectFileDialog::Listener,
+                            public printing::PrintViewManagerObserver {
  public:
   PrintPreviewHandler();
   virtual ~PrintPreviewHandler();
 
   // WebUIMessageHandler implementation.
   virtual void RegisterMessages();
 
   // SelectFileDialog::Listener implementation.
   virtual void FileSelected(const FilePath& path, int index, void* params);
   virtual void FileSelectionCanceled(void* params);
 
+  // PrintViewManagerObserver implementation.
+  virtual void OnPrintDialogShown();
+
   // Displays a modal dialog, prompting the user to select a file.
   void SelectFile(const FilePath& default_path);
 
+  // Called when the print preview tab navigates. This is the last time this
+  // this object has access to the PrintViewManager in order to disconnect the
+  // observer.
+  void OnNavigation();
+
  private:
   friend class PrintSystemTaskProxy;
 
   TabContents* preview_tab();
 
   // Get the default printer. |args| is unused.
   void HandleGetDefaultPrinter(const ListValue* args);
 
   // Get the list of printers. |args| is unused.
   void HandleGetPrinters(const ListValue* args);
@@ skipping 77 matching lines @@
   // Whether we have already logged a failed print preview.
   bool reported_failed_preview_;
 
   // Whether we have already logged the number of printers this session.
   bool has_logged_printers_count_;
 
   DISALLOW_COPY_AND_ASSIGN(PrintPreviewHandler);
 };
 
 #endif  // CHROME_BROWSER_UI_WEBUI_PRINT_PREVIEW_HANDLER_H_