Prerendered pages are swapped in at browser::Navigate time.

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 c6355229ebc06cfa4a38c2a4832df6aaccfb9e32..82ca15b52b42c3a42f5e60b4efc9635348015bee 100644
--- a/chrome/browser/prerender/prerender_contents.cc
+++ b/chrome/browser/prerender/prerender_contents.cc
@@ -21,7 +21,7 @@
 #include "chrome/browser/ui/tab_contents/tab_contents_wrapper.h"
 #include "chrome/common/chrome_notification_types.h"
 #include "chrome/common/icon_messages.h"
-#include "chrome/common/render_messages.h"
+#include "chrome/common/prerender_messages.h"
 #include "chrome/common/url_constants.h"
 #include "content/browser/in_process_webkit/session_storage_namespace.h"
 #include "content/browser/renderer_host/render_view_host.h"
@@ -62,6 +62,30 @@ struct PrerenderURLPredicate {
   GURL url_;
 };
 
+// Tells the render process at |child_id| whether |url| is a new prerendered
+// page, or whether |url| is being removed as a prerendered page. Currently
+// this will only inform the render process that created the prerendered page
+// with <link rel="prerender"> tags about it. This means that if a prerender
+// is created from the omnibox or from another page, clicking on the a link
+// for the same URL in another page will not swap in the prerender.

[dominich, 2012/02/29 18:32:01]

This isn't a problem for Omnibox as we cancel the prerender if the user
navigates somewhere other than we predicted already.

[cbentzel, 2012/02/29 19:22:36]

Done.

+void InformRenderProcessAboutPrerender(const GURL& url,

[dominich, 2012/02/29 18:32:01]

Given this is only called from methods in this class and |url| and |child_id|
are always |prerender_url_| and |creator_child_id_|, it would make more sense as
a private method of the class with a single bool parameter.

[cbentzel, 2012/02/29 19:22:36]

I like it here, because it means that if it changes I don't have to modify the
.h

[dominich, 2012/02/29 19:44:35]

Not modifying a header is a poor reason to base API decisions on. This should be
a class method as it uses state managed by the class. If it should change to be
more complex, then either more state will need to be added to the class, and
it's still correct, or it should be moved to a PrerenderBroadcaster class that
will have its own state.

[cbentzel, 2012/02/29 19:50:10]

Huh? It's a pretty stateless function, and does not directly modify any state
related to that class. That to me screams function.

+                                       bool is_add,
+                                       int child_id) {
+  if (child_id < 0)
+    return;
+  content::RenderProcessHost* render_process_host =
+      content::RenderProcessHost::FromID(child_id);
+  if (!render_process_host)
+    return;
+  IPC::Message* message = NULL;
+  if (is_add) {

[dominich, 2012/02/29 18:32:01]

nit: {} not required

[cbentzel, 2012/02/29 19:22:36]

Done.

+    message = new PrerenderMsg_AddPrerenderURL(url);
+  } else {
+    message = new PrerenderMsg_RemovePrerenderURL(url);
+  }
+  render_process_host->Send(message);
+}
+
 }  // end namespace
 
 class PrerenderContentsFactoryImpl : public PrerenderContents::Factory {
@@ -227,7 +251,8 @@ PrerenderContents::PrerenderContents(
       child_id_(-1),
       route_id_(-1),
       origin_(origin),
-      experiment_id_(experiment_id) {
+      experiment_id_(experiment_id),
+      creator_child_id_(-1) {
   DCHECK(prerender_manager != NULL);
 }
 
@@ -248,6 +273,12 @@ void PrerenderContents::StartPrerendering(
   DCHECK(prerender_contents_.get() == NULL);
 
   prerendering_has_started_ = true;
+  DCHECK(creator_child_id_ == -1);
+  if (source_render_view_host)
+    creator_child_id_ = source_render_view_host->process()->GetID();
+  InformRenderProcessAboutPrerender(prerender_url_, true,
+                                    creator_child_id_);
+
   WebContents* new_contents = WebContents::Create(
       profile_, NULL, MSG_ROUTING_NONE, NULL, session_storage_namespace);
   prerender_contents_.reset(new TabContentsWrapper(new_contents));
@@ -418,7 +449,7 @@ void PrerenderContents::Observe(int type,
         // first navigation, so there's no need to send the message just after
         // the TabContents is created.
         new_render_view_host->Send(
-            new ChromeViewMsg_SetIsPrerendering(
+            new PrerenderMsg_SetIsPrerendering(
                 new_render_view_host->routing_id(),
                 true));
 
@@ -543,6 +574,7 @@ bool PrerenderContents::ShouldSuppressDialogs() {
 }
 
 void PrerenderContents::Destroy(FinalStatus final_status) {
+  InformRenderProcessAboutPrerender(prerender_url_, false, creator_child_id_);
   if (prerendering_has_been_cancelled_)
     return;