[Mojo-Loading] Split too large data chunk in renderer

content/child/url_response_body_consumer.h

 // Copyright 2016 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_CHILD_URL_RESPONSE_BODY_CONSUMER_H_
 #define CONTENT_CHILD_URL_RESPONSE_BODY_CONSUMER_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 33 matching lines @@
   void OnComplete(const ResourceRequestCompletionStatus& status);
 
   // Cancels watching the handle and dispatches an error to the
   // ResourceDispatcher. This function does nothing if the reading is already
   // cancelled or done.
   void Cancel();
 
   void SetDefersLoading();
   void UnsetDefersLoading();
 
+  // The maximal number of bytes consumed in a task. When there are more bytes
+  // in the data pipe, they will be consumed in following tasks. Setting a too
+  // small number will generate ton of tasks but setting a too large number will
+  // lead to thread janks. Also, some clients cannot handle too large chunks
+  // (512k for example).
+  static constexpr uint32_t kMaxNumConsumedBytesInTask = 64 * 1024;
+
  private:
   friend class base::RefCounted<URLResponseBodyConsumer>;
   ~URLResponseBodyConsumer();
 
   class ReceivedData;
   void Reclaim(uint32_t size);
 
   void OnReadable(MojoResult unused);
   void NotifyCompletionIfAppropriate();
 
   const int request_id_;
   ResourceDispatcher* resource_dispatcher_;
   mojo::ScopedDataPipeConsumerHandle handle_;
   mojo::Watcher handle_watcher_;
   ResourceRequestCompletionStatus completion_status_;
   scoped_refptr<base::SingleThreadTaskRunner> task_runner_;
 
   bool has_received_completion_ = false;
   bool has_been_cancelled_ = false;
   bool has_seen_end_of_data_;
   bool is_deferred_ = false;
   bool is_in_on_readable_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(URLResponseBodyConsumer);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_CHILD_URL_RESPONSE_BODY_CONSUMER_H_