Implement a new flow event API that allows binding flow events and regular events.

ipc/ipc_channel_reader.cc

 // 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.
 
 #include "ipc/ipc_channel_reader.h"
 
 #include "ipc/ipc_listener.h"
 #include "ipc/ipc_logging.h"
 #include "ipc/ipc_message_macros.h"
 
@@ skipping 64 matching lines @@
     const char* message_tail = Message::FindNext(p, end);
     if (message_tail) {
       int len = static_cast<int>(message_tail - p);
       Message m(p, len);
       if (!WillDispatchInputMessage(&m))
         return false;
 
 #ifdef IPC_MESSAGE_LOG_ENABLED
       std::string name;
       Logging::GetInstance()->GetMessageText(m.type(), &name, &m, NULL);
-      TRACE_EVENT1("ipc,toplevel", "ChannelReader::DispatchInputData",
-                   "name", name);
+      TRACE_EVENT1_WITH_FLOW("ipc,toplevel", "ChannelReader::DispatchInputData",
+                   "name", name).APPEND_TRACE_EVENT_FLOW_END0(

[dsinclair, 2015/07/14 13:52:10]

Why do we have to l.APPEND a flow event? Why isn't it just part of the WITH_FLOW
API above?

This syntax isn't great it's hard to read and is going to be hard to use. Why
not do what was described in the doc and pass the id into WITH_FLOW?

+                   TRACE_DISABLED_BY_DEFAULT("ipc.flow"), "IPC",
+                   m.flags());
 #else
-      TRACE_EVENT2("ipc,toplevel", "ChannelReader::DispatchInputData",
+      TRACE_EVENT2_WITH_FLOW("ipc,toplevel", "ChannelReader::DispatchInputData",
                    "class", IPC_MESSAGE_ID_CLASS(m.type()),
-                   "line", IPC_MESSAGE_ID_LINE(m.type()));
+                   "line", IPC_MESSAGE_ID_LINE(m.type())).APPEND_TRACE_EVENT_FLOW_END0(
+                   TRACE_DISABLED_BY_DEFAULT("ipc.flow"), "IPC",
+                   m.flags());
 #endif
-      m.TraceMessageEnd();
       if (IsInternalMessage(m))
         HandleInternalMessage(m);
       else
         listener_->OnMessageReceived(m);
       if (m.dispatch_error())
         listener_->OnBadMessageReceived(m);
       p = message_tail;
     } else {
       // Last message is partial.
       break;
     }
   }
 
   // Save any partial data in the overflow buffer.
   input_overflow_buf_.assign(p, end - p);
 
   if (input_overflow_buf_.empty() && !DidEmptyInputBuffers())
     return false;
   return true;
 }
 
 
 }  // namespace internal
 }  // namespace IPC