Let prefetched resources skip cache revalidation once for a short duration.

net/http/http_cache.h

Index: net/http/http_cache.h
diff --git a/net/http/http_cache.h b/net/http/http_cache.h
index 1c1338b0d75d8019b82a5964609008b58d85ae0d..fee61d81d0a0839f2a7d66ff627dfe24f659fac8 100644
--- a/net/http/http_cache.h
+++ b/net/http/http_cache.h
@@ -37,6 +37,7 @@
 class GURL;
 
 namespace base {
+class Clock;
 class SingleThreadTaskRunner;
 }  // namespace base
 
@@ -52,6 +53,7 @@ class ChannelIDService;
 class DiskBasedCertCache;
 class HostResolver;
 class HttpAuthHandlerFactory;
+class HttpCachePrefetchValidationTest;
 class HttpNetworkSession;
 class HttpResponseInfo;
 class HttpServerProperties;
@@ -247,6 +249,7 @@ class NET_EXPORT HttpCache : public HttpTransactionFactory,
   class WorkItem;
   friend class Transaction;
   friend class ViewCacheHelper;
+  friend class HttpCachePrefetchValidationTest;
   struct PendingOp;  // Info for an entry under construction.
   class AsyncValidation;  // Encapsulates a single async revalidation.
 
@@ -271,6 +274,10 @@ class NET_EXPORT HttpCache : public HttpTransactionFactory,
   typedef std::set<ActiveEntry*> ActiveEntriesSet;
   typedef base::hash_map<std::string, int> PlaybackCacheMap;
 
+  // The number of minutes after a resource is prefetched that it can be used
+  // again without validation.
+  static const int kPrefetchReuseMins = 5;
+
   // Methods ------------------------------------------------------------------
 
   // Creates the |backend| object and notifies the |callback| when the operation
@@ -455,6 +462,9 @@ class NET_EXPORT HttpCache : public HttpTransactionFactory,
   // The async validations currently in progress, keyed by URL.
   AsyncValidationMap async_validations_;
 
+  // A clock that can be swapped out for testing.
+  scoped_ptr<base::Clock> clock_;
+
   base::WeakPtrFactory<HttpCache> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(HttpCache);