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

ui/events/latency_info.cc

Index: ui/events/latency_info.cc
diff --git a/ui/events/latency_info.cc b/ui/events/latency_info.cc
index 464883bfc688d882c2cb4eb7add9a9fc84a0df50..2e67372e992b1a21a4dd1a2853bc47b33ac558cc 100644
--- a/ui/events/latency_info.cc
+++ b/ui/events/latency_info.cc
@@ -303,6 +303,9 @@ void LatencyInfo::AddLatencyNumberWithTimestampImpl(
           ts);
     }
 
+    TRACE_EVENT_WITH_FLOW0("toplevel", "LatencyInfo::AddLatencyNumberWithTimestampImpl",
+                           TRACE_ID_DONT_MANGLE(trace_id),
+                           TRACE_EVENT_FLAG_FLOW_OUT);
     TRACE_EVENT_FLOW_BEGIN1(
         "input,benchmark", "LatencyInfo.Flow", TRACE_ID_DONT_MANGLE(trace_id),
         "trace_id", trace_id);
@@ -339,6 +342,9 @@ void LatencyInfo::AddLatencyNumberWithTimestampImpl(
                                   "data", AsTraceableData(*this));
     }
 
+    TRACE_EVENT_WITH_FLOW0("toplevel", "LatencyInfo::AddLatencyNumberWithTimestampImpl",
+                           TRACE_ID_DONT_MANGLE(trace_id),
+                           TRACE_EVENT_FLAG_FLOW_IN);
     TRACE_EVENT_FLOW_END_BIND_TO_ENCLOSING0(
         "input,benchmark", "LatencyInfo.Flow", TRACE_ID_DONT_MANGLE(trace_id));
   }