stale-while-revalidate experimental implementation.

net/http/http_cache_transaction.h

Index: net/http/http_cache_transaction.h
diff --git a/net/http/http_cache_transaction.h b/net/http/http_cache_transaction.h
index 8ba8f676cdefee3fa6e859a5211901a033d64cc4..08abd2d7ef9527b16167aa005216ae183d4bda29 100644
--- a/net/http/http_cache_transaction.h
+++ b/net/http/http_cache_transaction.h
@@ -16,6 +16,7 @@
 #include "net/base/request_priority.h"
 #include "net/http/http_cache.h"
 #include "net/http/http_request_headers.h"
+#include "net/http/http_response_headers.h"
 #include "net/http/http_response_info.h"
 #include "net/http/http_transaction.h"
 
@@ -108,6 +109,13 @@ class HttpCache::Transaction : public HttpTransaction {
     bypass_lock_for_test_ = true;
   }
 
+  // Used by asynchronous validations to ensure that the asynchronous validation
+  // path isn't re-entered. The LOAD_VALIDATE_CACHE flag cannot be passed to
+  // Start() via the HttpRequestInfo object because it has the side effect of
+  // causing HttpNetworkTransaction to add a Cache-Control: max-age=0 header.
+  // This method must be called before Start().
+  void ValidateInternalCache();
+
   // HttpTransaction methods:
   virtual int Start(const HttpRequestInfo* request_info,
                     const CompletionCallback& callback,
@@ -311,8 +319,9 @@ class HttpCache::Transaction : public HttpTransaction {
   // Returns network error code.
   int RestartNetworkRequestWithAuth(const AuthCredentials& credentials);
 
-  // Called to determine if we need to validate the cache entry before using it.
-  bool RequiresValidation();
+  // Called to determine if we need to validate the cache entry before using it,
+  // and whether the validation should be synchronous or asynchronous.
+  HttpResponseHeaders::ValidationType RequiredValidationType();
 
   // Called to make the request conditional (to ask the server if the cached
   // copy is valid).  Returns true if able to make the request conditional.
@@ -329,6 +338,9 @@ class HttpCache::Transaction : public HttpTransaction {
   // Removes content-length and byte range related info if needed.
   void FixHeadersForHead();
 
+  // Launches an asynchronous revalidation based on this transaction.
+  void TriggerAsyncValidation();
+
   // Changes the response code of a range request to be 416 (Requested range not
   // satisfiable).
   void FailRangeRequest();