Ensure that PageID's of prerendered pages do not exceed the Page ID of the

chrome/browser/prerender/prerender_contents.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/prerender/prerender_contents.h"
 
 #include <algorithm>
 #include <utility>
 
 #include "base/process_util.h"
@@ skipping 120 matching lines @@
       render_view_host_(NULL),
       prerender_url_(url),
       referrer_(referrer),
       profile_(profile),
       page_id_(0),
       ALLOW_THIS_IN_INITIALIZER_LIST(tab_contents_observer_registrar_(this)),
       has_stopped_loading_(false),
       final_status_(FINAL_STATUS_MAX),
       prerendering_has_started_(false),
       child_id_(-1),
-      route_id_(-1) {
+      route_id_(-1),
+      starting_page_id_(-1) {
   DCHECK(prerender_manager != NULL);
 }
 
 bool PrerenderContents::Init() {
   if (!AddAliasURL(prerender_url_))
     return false;
   return true;
 }
 
 // static
@@ skipping 103 matching lines @@
   prerender_contents_.reset(new TabContentsWrapper(new_contents));
   tab_contents_observer_registrar_.Observe(new_contents);
   prerender_contents_->download_tab_helper()->set_delegate(this);
 
   TabContents* source_tc =
       source_render_view_host->delegate()->GetAsTabContents();
   if (source_tc) {
     // So that history merging will work, get the max page ID
     // of the old page, and add a safety margin of 10 to it (for things
     // such as redirects).
-    int32 max_page_id = source_tc->GetMaxPageID();
-    if (max_page_id != -1) {
-      prerender_contents_->controller().set_max_restored_page_id(
-          max_page_id + 10);
-    }
+    starting_page_id_ = source_tc->GetMaxPageID();
+    if (starting_page_id_ < 0)
+      starting_page_id_ = 0;
+    starting_page_id_ += kPrerenderPageIdOffset;
+    prerender_contents_->controller().set_max_restored_page_id(
+        starting_page_id_);
 
     tab_contents_delegate_.reset(new TabContentsDelegateImpl(this));
     new_contents->set_delegate(tab_contents_delegate_.get());
 
     // Set the size of the new TC to that of the old TC.
     gfx::Rect tab_bounds;
     source_tc->view()->GetContainerBounds(&tab_bounds);
     prerender_contents_->view()->SizeContents(tab_bounds.size());
   }
 
@@ skipping 542 matching lines @@
   }
   return render_view_host_;
 }
 
 void PrerenderContents::CommitHistory(TabContents* tc) {
   if (tab_contents_delegate_.get())
     tab_contents_delegate_->CommitHistory(tc);
 }
 
 }  // namespace prerender