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

chrome/common/print_messages.h

Index: chrome/common/print_messages.h
diff --git a/chrome/common/print_messages.h b/chrome/common/print_messages.h
index 44de3e24d068969bd48fb4c449eecf0db4b47558..cb29ad1cddd2b3b555bbd6d6134817a340e38dd7 100644
--- a/chrome/common/print_messages.h
+++ b/chrome/common/print_messages.h
@@ -178,6 +178,9 @@ 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.