Prerender/Instant interopability.

chrome/browser/prerender/prerender_contents.cc

Index: chrome/browser/prerender/prerender_contents.cc
diff --git a/chrome/browser/prerender/prerender_contents.cc b/chrome/browser/prerender/prerender_contents.cc
index 343c61a163de4cad8b5f84f4678f74498d6d3534..bbe780638f0cceddafe715b50fa3dca6281720c9 100644
--- a/chrome/browser/prerender/prerender_contents.cc
+++ b/chrome/browser/prerender/prerender_contents.cc
@@ -33,6 +33,7 @@
 #include "content/browser/site_instance.h"
 #include "content/browser/tab_contents/tab_contents_delegate.h"
 #include "content/browser/tab_contents/tab_contents_view.h"
+#include "content/common/content_constants.h"
 #include "content/common/notification_service.h"
 #include "content/common/view_messages.h"
 #include "ui/gfx/rect.h"
@@ -257,14 +258,12 @@ void PrerenderContents::StartPrerendering(
   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);
-    }
+    // So that history merging will work, set the max page ID to one greater
+    // than the largest we can ever have. This allows for redirects, but also
+    // for any tabs the user may open between us rendering this page and
+    // swapping it in.
+    prerender_contents_->controller().set_max_restored_page_id(
+        content::kMaxSessionHistoryEntries + 1);
 
     tab_contents_delegate_.reset(new TabContentsDelegateImpl(this));
     new_contents->set_delegate(tab_contents_delegate_.get());