Make three simultanious prerenders the default maximum in Canary and Dev only.

chrome/browser/prerender/prerender_config.h

Index: chrome/browser/prerender/prerender_config.h
diff --git a/chrome/browser/prerender/prerender_config.h b/chrome/browser/prerender/prerender_config.h
index 04f244b3e184bb849296e8533576b19d9d421336..6c0136b0f0eb454148dcf6b86b28d7c01a24bd58 100644
--- a/chrome/browser/prerender/prerender_config.h
+++ b/chrome/browser/prerender/prerender_config.h
@@ -5,6 +5,8 @@
 #ifndef CHROME_BROWSER_PRERENDER_PRERENDER_CONFIG_H_
 #define CHROME_BROWSER_PRERENDER_PRERENDER_CONFIG_H_
 
+#include <string>
+
 #include "base/time.h"
 #include "ui/gfx/rect.h"
 
@@ -17,7 +19,8 @@ struct Config {
   size_t max_bytes;
 
   // Number of simultaneous prendered pages allowed.
-  unsigned int max_elements;
+  static const size_t kMaximumMaxConcurrency = 3;

[dominich, 2012/07/23 18:45:56]

This isn't referenced. PrerenderManager sets '3' explicitly.

I'm ok with that, but you should remove this.

[gavinp, 2012/07/23 18:51:55]

See
http://codereview.chromium.org/10802024/diff/15001/chrome/browser/prerender/p...
, line 167. The histogram has to be sized right, or it's wasting RAM.

[dominich, 2012/07/23 18:57:14]

I see. maybe instead of an enum you should be using UMA_HISTOGRAM_COUNTS ?

[gavinp, 2012/07/23 19:06:10]

Well, that's just giving up and wasting a lot more memory. UMA_HISTOGRAM_COUNTS
always uses 50 buckets. I have actually been changing our uses of COUNTS away
from that, just as a quick CL to save memory. I have added a constant here, and
now I'm DCHECKing on that. That should be good enough to have us resize the
histogram when we need to.

+  size_t max_concurrency;
 
   // Is rate limiting enabled?
   bool rate_limit_enabled;
@@ -42,3 +45,4 @@ struct Config {
 }  // namespace prerender
 
 #endif  // CHROME_BROWSER_PRERENDER_PRERENDER_CONFIG_H_
+