Have MimeSniffingResourceHandler call WillStartRequest on new Handlers.

content/browser/loader/mime_sniffing_resource_handler.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CONTENT_BROWSER_LOADER_MIME_SNIFFING_RESOURCE_HANDLER_H_
 #define CONTENT_BROWSER_LOADER_MIME_SNIFFING_RESOURCE_HANDLER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 46 matching lines @@
     // received.
     STATE_STARTING,
 
     // In this state, the MimeSniffingResourceHandler is buffering the response
     // data in read_buffer_, waiting to sniff the mime type and make a choice
     // about request interception.
     STATE_BUFFERING,
 
     // In this state, the MimeSniffingResourceHandler has identified the mime
     // type and made a decision on whether the request should be intercepted or
-    // not. It is nows attempting to replay the response to downstream
-    // handlers.
-    STATE_INTERCEPTION_CHECK_DONE,
+    // not.  It now needs to prepare the new handler for use, and replay the
+    // already received data.
+    STATE_NEED_TO_PREPARE_TO_USE_NEW_HANDLER,
+
+    // In this state, the MimeSniffingResourceHandler is preparing the new
+    // handler for use.
+    STATE_PREPARING_TO_USE_NEW_HANDLER,
 
     // In this state, the MimeSniffingResourceHandler is replaying the buffered
     // OnResponseStarted event to the downstream ResourceHandlers.
-    STATE_REPLAYING_RESPONSE_RECEIVED,
+    STATE_REPLAYING_RECEIVED_RESPONSE,
 
     // In this state, the MimeSniffingResourceHandler is just a blind
     // pass-through
     // ResourceHandler.
     STATE_STREAMING,
   };
 
   // ResourceHandler implementation:
   void SetController(ResourceController* controller) override;
   bool OnWillStart(const GURL&, bool* defer) override;
@@ skipping 17 matching lines @@
   // true otherwise. Each of them will set |defer| to true if the request will
   // proceed to the next stage asynchronously.
 
   // Used to advance through the states of the state machine.
   void AdvanceState();
   bool ProcessState(bool* defer);
 
   // Intercepts the request as a stream/download if needed.
   bool MaybeIntercept(bool* defer);
 
+  // Prepares the new handler for use, advancing it to a state where it can
+  // be swapped in to replace the InterceptingResourceHandler's old one.
+  bool PrepareToUseNewHandler(bool* defer);
+
   // Replays OnResponseStarted on the downstream handlers.
-  bool ReplayResponseReceived(bool* defer);
+  bool ReplayReceivedResponse(bool* defer);
 
   // Replays OnReadCompleted on the downstreams handlers.
   bool ReplayReadCompleted(bool* defer);
 
   // --------------------------------------------------------------------------
 
   // Whether the response body should be sniffed in order to determine the MIME
   // type of the response.
   bool ShouldSniffContent();
 
@@ skipping 39 matching lines @@
   scoped_refptr<net::IOBuffer> read_buffer_;
   int read_buffer_size_;
   int bytes_read_;
 
   // The InterceptingResourceHandler that will perform ResourceHandler swap if
   // needed.
   InterceptingResourceHandler* intercepting_handler_;
 
   RequestContextType request_context_type_;
 
+  std::unique_ptr<ResourceHandler> new_handler_;
+  std::string payload_for_old_handler_;
+
   base::WeakPtrFactory<MimeSniffingResourceHandler> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MimeSniffingResourceHandler);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_LOADER_MIME_SNIFFING_RESOURCE_HANDLER_H_