HttpCache::Transaction layer allowing parallel validation

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 51c0db70256cbd31505ca20ffba6486ab4c36aad..ead9395207a7b8f5e137bf420f480b4cc4b44616 100644
--- a/net/http/http_cache_transaction.h
+++ b/net/http/http_cache_transaction.h
@@ -164,6 +164,10 @@ class HttpCache::Transaction : public HttpTransaction {
   int ResumeNetworkStart() override;
   void GetConnectionAttempts(ConnectionAttempts* out) const override;
 
+  // Invoked when parallel validation cannot proceed due to response failure
+  // and this transaction needs to be restarted.
+  void SetValidatingCannotProceed();
+
   // Returns the estimate of dynamically allocated memory in bytes.
   size_t EstimateMemoryUsage() const;
 
@@ -220,6 +224,9 @@ class HttpCache::Transaction : public HttpTransaction {
     STATE_PARTIAL_HEADERS_RECEIVED,
     STATE_CACHE_READ_METADATA,
     STATE_CACHE_READ_METADATA_COMPLETE,
+    STATE_HEADERS_PHASE_CANNOT_PROCEED,
+    STATE_FINISH_HEADERS,
+    STATE_FINISH_HEADERS_COMPLETE,
 
     // These states are entered from Read/AddTruncatedFlag.
     STATE_NETWORK_READ,
@@ -286,6 +293,9 @@ class HttpCache::Transaction : public HttpTransaction {
   int DoTruncateCachedMetadata();
   int DoTruncateCachedMetadataComplete(int result);
   int DoPartialHeadersReceived();
+  int DoHeadersPhaseCannotProceed();
+  int DoFinishHeaders(int result);
+  int DoFinishHeadersComplete(int result);
   int DoCacheReadMetadata();
   int DoCacheReadMetadataComplete(int result);
   int DoNetworkRead();
@@ -430,7 +440,12 @@ class HttpCache::Transaction : public HttpTransaction {
   void SyncCacheEntryStatusToResponse();
   void RecordHistograms();
 
-  // Called to signal completion of asynchronous IO.
+  // Called to signal completion of asynchronous IO. Note that this callback is
+  // used in the conventional sense where one layer calls the callback of the
+  // layer above it e.g. this callback gets called from the network transaction
+  // layer. In addition, it is also used for HttpCache layer to let this
+  // transaction know when it is out of a queued state in ActiveEntry and can
+  // continue its processing.
   void OnIOComplete(int result);
 
   // When in a DoLoop, use this to set the next state as it verifies that the
@@ -456,6 +471,7 @@ class HttpCache::Transaction : public HttpTransaction {
   const HttpResponseInfo* new_response_;
   std::string cache_key_;
   Mode mode_;
+  Mode original_mode_;  // Used when restarting the transaction.
   bool reading_;  // We are already reading. Never reverts to false once set.
   bool invalid_range_;  // We may bypass the cache for this request.
   bool truncated_;  // We don't have all the response data.