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

ipc/ipc_channel_reader.cc

Index: ipc/ipc_channel_reader.cc
diff --git a/ipc/ipc_channel_reader.cc b/ipc/ipc_channel_reader.cc
index f41a0d7737e4656cd279db0de8ef83c2b9e9fbaa..81e66011a1be68c8416460304327089d689e5f30 100644
--- a/ipc/ipc_channel_reader.cc
+++ b/ipc/ipc_channel_reader.cc
@@ -82,14 +82,17 @@ bool ChannelReader::DispatchInputData(const char* input_data,
 #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