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

base/trace_event/trace_event_impl.h

Index: base/trace_event/trace_event_impl.h
diff --git a/base/trace_event/trace_event_impl.h b/base/trace_event/trace_event_impl.h
index ccb850033e1926d59ff4396b8a9bb36acf61a109..f89f53a1e0bee3b002098d19452717f97fb3746a 100644
--- a/base/trace_event/trace_event_impl.h
+++ b/base/trace_event/trace_event_impl.h
@@ -104,6 +104,10 @@ class BASE_EXPORT TraceEvent {
   TraceEvent();
   ~TraceEvent();
 
+  void appendFlowEvent(TraceEvent *flowEvent) {
+    flowEvent_ = flowEvent;
+  }
+
   // We don't need to copy TraceEvent except when TraceEventBuffer is cloned.
   // Use explicit copy method to avoid accidentally misuse of copy.
   void CopyFrom(const TraceEvent& other);
@@ -149,6 +153,7 @@ class BASE_EXPORT TraceEvent {
   TimeDelta thread_duration() const { return thread_duration_; }
   unsigned long long id() const { return id_; }
   unsigned char flags() const { return flags_; }
+  bool isFlowEvent() const;
 
   // Exposed for unittesting:
 
@@ -185,6 +190,7 @@ class BASE_EXPORT TraceEvent {
   char phase_;
   unsigned char flags_;
   unsigned char arg_types_[kTraceMaxNumArgs];
+  TraceEvent *flowEvent_;
 
   DISALLOW_COPY_AND_ASSIGN(TraceEvent);
 };
@@ -709,6 +715,32 @@ class BASE_EXPORT TraceLog : public MemoryDumpProvider {
   DISALLOW_COPY_AND_ASSIGN(TraceLog);
 };
 
+class TraceEventHandleWrapper {
+public:
+  TraceEventHandleWrapper() {
+    handle_ = {0, 0, 0};
+    event_ = NULL;
+  }
+  TraceEventHandleWrapper(TraceEventHandle h) {
+    handle_ = h;
+    TraceLog* tracer = base::trace_event::TraceLog::GetInstance();
+    event_ = tracer->GetEventByHandle(h);
+  }
+
+  void appendFlowEvent(TraceEventHandle h) {
+    if (event_) {
+      TraceLog* tracer = base::trace_event::TraceLog::GetInstance();
+      TraceEvent *flowEvent = tracer->GetEventByHandle(h);
+      event_->appendFlowEvent(flowEvent);
+    }
+  }
+
+private:
+  TraceEventHandle handle_;
+  TraceEvent *event_;
+};
+
+
 }  // namespace trace_event
 }  // namespace base