Make ResourceHandler::OnWillRead able to complete asynchronously.

content/browser/loader/mime_sniffing_resource_handler.h

Index: content/browser/loader/mime_sniffing_resource_handler.h
diff --git a/content/browser/loader/mime_sniffing_resource_handler.h b/content/browser/loader/mime_sniffing_resource_handler.h
index 47a9dff945be4094ffa8b406af212c50c7e56dfb..21200938cb7bb5e76a8fb4c2832d8696d3c05cf9 100644
--- a/content/browser/loader/mime_sniffing_resource_handler.h
+++ b/content/browser/loader/mime_sniffing_resource_handler.h
@@ -66,6 +66,11 @@ class CONTENT_EXPORT MimeSniffingResourceHandler
     // about request interception.
     STATE_BUFFERING,
 
+    // In these states, the MimeSniffingResourceHandler is calling OnWillRead on
+    // the downstream ResourceHandler and then waiting for the response.
+    STATE_CALLING_ON_WILL_READ,
+    STATE_WAITING_FOR_BUFFER,
+
     // 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
@@ -88,8 +93,9 @@ class CONTENT_EXPORT MimeSniffingResourceHandler
   void OnResponseStarted(
       ResourceResponse* response,
       std::unique_ptr<ResourceController> controller) override;
-  bool OnWillRead(scoped_refptr<net::IOBuffer>* buf,
-                  int* buf_size) override;
+  void OnWillRead(scoped_refptr<net::IOBuffer>* buf,
+                  int* buf_size,
+                  std::unique_ptr<ResourceController> controller) override;
   void OnReadCompleted(int bytes_read,
                        std::unique_ptr<ResourceController> controller) override;
   void OnResponseCompleted(
@@ -110,6 +116,12 @@ class CONTENT_EXPORT MimeSniffingResourceHandler
   // Intercepts the request as a stream/download if needed.
   void MaybeIntercept();
 
+  // Calls OnWillRead on the downstream handlers.
+  void CallOnWillRead();
+
+  // Copies received buffer to parent.
+  void BufferReceived();
+
   // Replays OnResponseStarted on the downstream handlers.
   void ReplayResponseReceived();
 
@@ -167,6 +179,11 @@ class CONTENT_EXPORT MimeSniffingResourceHandler
   int read_buffer_size_;
   int bytes_read_;
 
+  // Pointers to parent-owned read buffer and its size.  Only used for first
+  // OnWillRead call.
+  scoped_refptr<net::IOBuffer>* parent_read_buffer_;
+  int* parent_read_buffer_size_;
+
   // The InterceptingResourceHandler that will perform ResourceHandler swap if
   // needed.
   InterceptingResourceHandler* intercepting_handler_;