Limit prerender by only allowing one every X ms (X currently set to 500).

chrome/browser/prerender/prerender_manager.h

Index: chrome/browser/prerender/prerender_manager.h
diff --git a/chrome/browser/prerender/prerender_manager.h b/chrome/browser/prerender/prerender_manager.h
index fa53ae79abb3395633baf76926cf30513bda4845..65a245fcccdbcb9cd9c82bb3e157ed3f7479330a 100644
--- a/chrome/browser/prerender/prerender_manager.h
+++ b/chrome/browser/prerender/prerender_manager.h
@@ -97,6 +97,10 @@ class PrerenderManager : public base::RefCounted<PrerenderManager> {
   void MarkTabContentsAsNotPrerendered(TabContents* tc);
   bool IsTabContentsPrerendered(TabContents* tc) const;
 
+  static void set_rate_limit_enabled(bool enable) {
+    rate_limit_enabled_ = enable;
+  }
+
  protected:
   virtual ~PrerenderManager();
 
@@ -136,6 +140,8 @@ class PrerenderManager : public base::RefCounted<PrerenderManager> {
 
   static void RecordPrefetchTagObservedOnUIThread();
 
+  static bool DoesRateLimitAllowPrerender();
+
   Profile* profile_;
 
   base::TimeDelta max_prerender_age_;
@@ -160,6 +166,9 @@ class PrerenderManager : public base::RefCounted<PrerenderManager> {
   // Time interval at which periodic cleanups are performed.
   static const int kPeriodicCleanupIntervalMs = 1000;
 
+  // Time interval before a new prerender is allowed.
+  static const int kMinTimeBetweenPrerendersMs = 500;

[tburkard, 2011/03/11 22:57:40]

I think we should set this to 1s.

[dominich, 2011/03/11 23:14:57]

I originally had it at 1s but felt it was too long. I did some vaguely empirical
testing by running searches and could easily get two searches in under 1s.

As this is only meant to catch a situation where we're being flooded, I felt
that 500 was a good balance. Do you have reason to think otherwise?

+
   scoped_ptr<PrerenderContents::Factory> prerender_contents_factory_;
 
   static PrerenderManagerMode mode_;
@@ -174,6 +183,11 @@ class PrerenderManager : public base::RefCounted<PrerenderManager> {
   // pages.
   base::RepeatingTimer<PrerenderManager> repeating_timer_;
 
+  // Track time of last prerender to limit prerender spam.
+  // TODO(dominich): This could be an average rate instead of a single time
+  static base::TimeTicks last_prerender_start_time_;
+  static bool rate_limit_enabled_;
+
   DISALLOW_COPY_AND_ASSIGN(PrerenderManager);
 };