Print Preview: Make preview generation event driven to eliminate synchronous messages.

chrome/browser/ui/webui/print_preview_ui.cc

 // 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.
 
 #include "chrome/browser/ui/webui/print_preview_ui.h"
 
 #include "base/metrics/histogram.h"
 #include "base/string_util.h"
 #include "base/values.h"
 #include "chrome/browser/printing/print_preview_data_service.h"
 #include "chrome/browser/profiles/profile.h"
 #include "chrome/browser/ui/webui/print_preview_data_source.h"
 #include "chrome/browser/ui/webui/print_preview_handler.h"
 #include "content/browser/tab_contents/tab_contents.h"
 
 PrintPreviewUI::PrintPreviewUI(TabContents* contents)
     : ChromeWebUI(contents),
       initial_preview_start_time_(base::TimeTicks::Now()),
-      request_count_(0U) {
+      request_count_(0U),
+      document_cookie_(0) {
   // WebUI owns |handler_|.
   handler_ = new PrintPreviewHandler();
   AddMessageHandler(handler_->Attach(this));
 
   // Set up the chrome://print/ data source.
   contents->profile()->GetChromeURLDataManager()->AddDataSource(
       new PrintPreviewDataSource());
 
   // Store the PrintPreviewUIAddress as a string.
   // "0x" + deadc0de + '\0' = 2 + 2 * sizeof(this) + 1;
@@ skipping 17 matching lines @@
 void PrintPreviewUI::OnInitiatorTabClosed(
     const std::string& initiator_url) {
   StringValue initiator_tab_url(initiator_url);
   CallJavascriptFunction("onInitiatorTabClosed", initiator_tab_url);
 }
 
 void PrintPreviewUI::OnPrintPreviewRequest() {
   request_count_++;
 }
 
-void PrintPreviewUI::OnDidGetPreviewPageCount(int page_count) {
+void PrintPreviewUI::OnDidGetPreviewPageCount(int document_cookie,
+                                              int page_count) {
   DCHECK_GT(page_count, 0);
+  document_cookie_ = document_cookie;
   FundamentalValue count(page_count);
   CallJavascriptFunction("onDidGetPreviewPageCount", count);
 }
 
 void PrintPreviewUI::OnDidPreviewPage(int page_number) {
   DCHECK_GE(page_number, 0);
   FundamentalValue number(page_number);
   CallJavascriptFunction("onDidPreviewPage", number);
 }
 
@@ skipping 40 matching lines @@
 
 bool PrintPreviewUI::HasPendingRequests() {
   return request_count_ > 1;
 }
 
 PrintPreviewDataService* PrintPreviewUI::print_preview_data_service() {
   return PrintPreviewDataService::GetInstance();
 }
 
 void PrintPreviewUI::DecrementRequestCount() {
-  DCHECK_GT(request_count_, 0U);
   if (request_count_ > 0)
     request_count_--;
 }
+
+int PrintPreviewUI::document_cookie() {
+  return document_cookie_;
+}