Modify AsyncResourceHandler to use a single shared memory buffer (in ring

content/common/resource_messages.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.
 
 // IPC messages for resource loading.
 
 // Multiply-included message file, hence no include guard.
 #include "base/shared_memory.h"
 #include "content/public/common/common_param_traits.h"
 #include "content/public/common/resource_response.h"
@@ skipping 138 matching lines @@
                     int64 /* size */)
 
 // Sent when the request has been redirected.  The receiver is expected to
 // respond with either a FollowRedirect message (if the redirect is to be
 // followed) or a CancelRequest message (if it should not be followed).
 IPC_MESSAGE_ROUTED3(ResourceMsg_ReceivedRedirect,
                     int /* request_id */,
                     GURL /* new_url */,
                     content::ResourceResponseHead)
 
-// Sent when some data from a resource request is ready. The handle should
-// already be mapped into the process that receives this message.
+// Sent to set the shared memory buffer to be used to transmit response data to
+// the renderer.  Subsequent DataReceived messages refer to byte ranges in the
+// shared memory buffer.  The shared memory buffer should be retained by the
+// renderer until the resource request completes.
+//
+// NOTE: The shared memory handle should already be mapped into the process
+// that receives this message.
+//
+IPC_MESSAGE_ROUTED3(ResourceMsg_SetDataBuffer,
+                    int /* request_id */,
+                    base::SharedMemoryHandle /* shm_handle */,
+                    int /* shm_size */)
+
+// Sent when some data from a resource request is ready.  The data offset and
+// length specify a byte range into the shared memory buffer provided by the
+// SetDataBuffer message.
 IPC_MESSAGE_ROUTED4(ResourceMsg_DataReceived,
                     int /* request_id */,
-                    base::SharedMemoryHandle /* data */,
-                    int /* data_len */,
+                    int /* data_offset */,
+                    int /* data_length */,
                     int /* encoded_data_length */)
 
 // Sent when some data from a resource request has been downloaded to
 // file. This is only called in the 'download_to_file' case and replaces
 // ResourceMsg_DataReceived in the call sequence in that case.
 IPC_MESSAGE_ROUTED2(ResourceMsg_DataDownloaded,
                     int /* request_id */,
                     int /* data_len */)
 
 // Sent when the request has been completed.
@@ skipping 38 matching lines @@
                     int /* request_id */)
 
 // Sent by the renderer process to acknowledge receipt of a
 // UploadProgress message.
 IPC_MESSAGE_ROUTED1(ResourceHostMsg_UploadProgress_ACK,
                     int /* request_id */)
 
 // Sent when the renderer process deletes a resource loader.
 IPC_MESSAGE_CONTROL1(ResourceHostMsg_ReleaseDownloadedFile,
                      int /* request_id */)