Add GetExpirationTimes() to HttpResponseHeader.

net/http/http_cache_transaction.cc

Index: net/http/http_cache_transaction.cc
diff --git a/net/http/http_cache_transaction.cc b/net/http/http_cache_transaction.cc
index 15ad924df8f846599166ad663f6c01d3b3dbe94c..ee8ea32b970095e4cb949cc1483bcb5339e0c615 100644
--- a/net/http/http_cache_transaction.cc
+++ b/net/http/http_cache_transaction.cc
@@ -1995,12 +1995,10 @@ bool HttpCache::Transaction::RequiresValidation() {
   if (request_->method == "PUT" || request_->method == "DELETE")
     return true;
 
-  if (response_.headers->RequiresValidation(
-          response_.request_time, response_.response_time, Time::Now())) {
-    return true;
-  }
-
-  return false;
+  const Time freshness_expiry =
+      response_.headers->GetFreshnessExpiry(response_.request_time,
+                                            response_.response_time);
+  return freshness_expiry <= Time::Now();
 }
 
 bool HttpCache::Transaction::ConditionalizeRequest() {