Cancel loading when body stream reader is detached.

content/child/shared_memory_data_consumer_handle.h

Index: content/child/shared_memory_data_consumer_handle.h
diff --git a/content/child/shared_memory_data_consumer_handle.h b/content/child/shared_memory_data_consumer_handle.h
index 6d74178f5cda317e5fdc1e0c6e85e5d92756ad25..869aed2f95ed6ada82092ca545b2099d3cb91a7a 100644
--- a/content/child/shared_memory_data_consumer_handle.h
+++ b/content/child/shared_memory_data_consumer_handle.h
@@ -5,6 +5,7 @@
 #ifndef CONTENT_CHILD_SHARED_MEMORY_DATA_CONSUMER_HANDLE_H_
 #define CONTENT_CHILD_SHARED_MEMORY_DATA_CONSUMER_HANDLE_H_
 
+#include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "content/common/content_export.h"
@@ -59,8 +60,18 @@ class CONTENT_EXPORT SharedMemoryDataConsumerHandle final
     DISALLOW_COPY_AND_ASSIGN(ReaderImpl);
  };
 
+  // Creates a handle and a writer associated with the handle. The created
+  // writer should be used on the calling thread.
   SharedMemoryDataConsumerHandle(BackpressureMode mode,
                                  scoped_ptr<Writer>* writer);
+  // |on_reader_detached| will be called aynchronously on the calling thread
+  // when the reader (including the handle) is detached (i.e. both the handle
+  // and the reader are destructed). The callback will be reset in the internal
+  // context when the writer is detached, i.e. |Close| or |Fail| is called,
+  // and the callback will never be called.
+  SharedMemoryDataConsumerHandle(BackpressureMode mode,
+                                 const base::Closure& on_reader_detached,
+                                 scoped_ptr<Writer>* writer);
   virtual ~SharedMemoryDataConsumerHandle();
 
   scoped_ptr<Reader> ObtainReader(Client* client);