Change multi-prerender API to include per launcher slots.

chrome/browser/predictors/autocomplete_action_predictor.cc

Index: chrome/browser/predictors/autocomplete_action_predictor.cc
diff --git a/chrome/browser/predictors/autocomplete_action_predictor.cc b/chrome/browser/predictors/autocomplete_action_predictor.cc
index 291bbd67c8eafc5285351e072868d818beacceaa..fbfe1919ebe0306e3fa3f4efd4e6f10dc65535d4 100644
--- a/chrome/browser/predictors/autocomplete_action_predictor.cc
+++ b/chrome/browser/predictors/autocomplete_action_predictor.cc
@@ -140,8 +140,8 @@ void AutocompleteActionPredictor::StartPrerendering(
     const GURL& url,
     const content::SessionStorageNamespaceMap& session_storage_namespace_map,
     const gfx::Size& size) {
-  if (prerender_handle_.get())
-    prerender_handle_->OnNavigateAway();
+  if (prerender_handle_)
+    prerender_handle_->OnCancel();

[mmenke, 2012/12/28 18:25:33]

Hmm...  Calling "OnCancel" to cancel something is a little strange.  Suppose the
naming makes the most sense, though, as long as OnNavigateAway is also a
PrerenderHandle function.

Suggestion for a later CL:  Since OnNavigateAway is a <channel
user="jam">prerender link concept, not a general prerender concept</channel>, we
may want to structure things to get rid of the function, and just have
PrerenderLinkManager doing something like calling
"PrerenderManager::UpdateTimeoutForPrerender" or some such, and renaming this
function to Cancel().

We should put some thought into the division of labor between the two *Manager
classes.

[gavinp, 2012/12/28 19:53:46]

Yes. I think this series of CLs has cleaned up the existing behaviour some on
the whole, but introduced enough new behaviour that things are probably as
confusing as before (if not more). Separating the link manager out more could be
a good way to go.

I've also considered splitting the prerender manager into the prerender
interface (the prerender link manager + some stuff) and prerender-runner. Those
two phases are related, but that split would certainly make life easier for
consumers, and we could then re-unify the interface for omnibox/local prerenders
and links.

   if (prerender::PrerenderManager* prerender_manager =
           prerender::PrerenderManagerFactory::GetForProfile(profile_)) {
     content::SessionStorageNamespace* session_storage_namespace = NULL;