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

base/trace_event/trace_event_impl.cc

Index: base/trace_event/trace_event_impl.cc
diff --git a/base/trace_event/trace_event_impl.cc b/base/trace_event/trace_event_impl.cc
index 1fc22565d0ec182e1e908abb40f36921846f23bb..71e64239f3b7cff38b20438321dddf71e5b33a95 100644
--- a/base/trace_event/trace_event_impl.cc
+++ b/base/trace_event/trace_event_impl.cc
@@ -602,6 +602,7 @@ void TraceEvent::Initialize(
   thread_id_ = thread_id;
   phase_ = phase;
   flags_ = flags;
+  flowEvent_ = NULL;
 
   // Clamp num_args since it may have been set by a third_party library.
   num_args = (num_args > kTraceMaxNumArgs) ? kTraceMaxNumArgs : num_args;
@@ -862,6 +863,12 @@ void TraceEvent::AppendAsJSON(
     StringAppendF(out, ",\"s\":\"%c\"", scope);
   }
 
+  // Output flow event info if there is any
+  if (flowEvent_) {
+    StringAppendF(out, ",\"flow\":");
+    flowEvent_->AppendAsJSON(out, argument_filter_predicate);
+  }
+
   *out += "}";
 }
 
@@ -888,6 +895,12 @@ void TraceEvent::AppendPrettyPrinted(std::ostringstream* out) const {
   }
 }
 
+bool TraceEvent::isFlowEvent() const {
+  return ((phase() == TRACE_EVENT_PHASE_FLOW_BEGIN) ||
+          (phase() == TRACE_EVENT_PHASE_FLOW_STEP) ||
+          (phase() == TRACE_EVENT_PHASE_FLOW_END));
+}
+
 ////////////////////////////////////////////////////////////////////////////////
 //
 // TraceResultBuffer
@@ -1851,6 +1864,11 @@ void TraceLog::ConvertTraceEventsToTraceFormat(
   scoped_refptr<RefCountedString> json_events_str_ptr = new RefCountedString();
   while (const TraceBufferChunk* chunk = logged_events->NextChunk()) {
     for (size_t j = 0; j < chunk->size(); ++j) {
+      // Flow Events are always bundled to regular events, and will be handled
+      // within their bundled events.
+      if (chunk->GetEventAt(j)->isFlowEvent())
+        continue;
+
       size_t size = json_events_str_ptr->size();
       if (size > kTraceEventBufferSizeInBytes) {
         flush_output_callback.Run(json_events_str_ptr, true);