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

chrome/common/print_messages.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.
 
 // IPC messages for printing.
 // Multiply-included message file, hence no include guard.
 
 #include "base/values.h"
 #include "base/shared_memory.h"
 #include "ipc/ipc_message_macros.h"
@@ skipping 160 matching lines @@
                            base::SharedMemoryHandle /* renderer handle */,
                            base::SharedMemoryHandle /* browser handle */)
 #endif
 
 // Tells the browser that the renderer is done calculating the number of
 // rendered pages according to the specified settings.
 IPC_MESSAGE_ROUTED2(PrintHostMsg_DidGetPrintedPagesCount,
                     int /* rendered document cookie */,
                     int /* number of rendered pages */)
 
+// Tells the browser that the print dialog has been shown.
+IPC_MESSAGE_ROUTED0(PrintHostMsg_DidShowPrintDialog)

[Lei Zhang, 2011/06/21 01:54:46]

You can avoid adding a new message, the additional IPC and the associated
PrintWebViewHelper / PrintViewManager changes, if you just instead add a call to
print_job_manager_->OnDidShowPrintDialog() in
PrintingMessageFilter::OnScriptedPrint() to keep this all on the browser side.

[James Hawkins, 2011/06/22 23:47:24]

There are several reasons why this doesn't work:
* PrintJobManager has no access to the PrintViewManagerDelegate.
* Currently OnScriptedPrint is the only initiator of the code path to show the
native print dialog for settings, but that may not always be the case in the
future: this notification is designed to be sent in all cases where the native
print dialog is shown. Moving the notification to OnScriptedPrint is fragile in
this sense.

+
 // Sends back to the browser the rendered "printed page" that was requested by
 // a ViewMsg_PrintPage message or from scripted printing. The memory handle in
 // this message is already valid in the browser process.
 IPC_MESSAGE_ROUTED1(PrintHostMsg_DidPrintPage,
                     PrintHostMsg_DidPrintPage_Params /* page content */)
 
 // The renderer wants to know the default print settings.
 IPC_SYNC_MESSAGE_ROUTED0_1(PrintHostMsg_GetDefaultPrintSettings,
                            PrintMsg_Print_Params /* default_settings */)
 
@@ skipping 32 matching lines @@
 IPC_MESSAGE_ROUTED1(PrintHostMsg_PagesReadyForPreview,
                     PrintHostMsg_DidPreviewDocument_Params /* params */)
 
 // Tell the browser printing failed.
 IPC_MESSAGE_ROUTED1(PrintHostMsg_PrintingFailed,
                     int /* document cookie */)
 
 // Tell the browser print preview failed.
 IPC_MESSAGE_ROUTED1(PrintHostMsg_PrintPreviewFailed,
                     int /* document cookie */)