LatencyInfo trace_id_ no longer dependent on sequence_number.

ui/latency/latency_info.h

Index: ui/latency/latency_info.h
diff --git a/ui/latency/latency_info.h b/ui/latency/latency_info.h
index 0f8b6be29ff6b45f316635ff3f9ee88a84281872..2dcf550ec3823b3519275847d26b477f7c050886 100644
--- a/ui/latency/latency_info.h
+++ b/ui/latency/latency_info.h
@@ -208,10 +208,12 @@ class LatencyInfo {
     source_event_type_ = type;
   }
 
+  bool began() const { return began_; }
   bool terminated() const { return terminated_; }
   void set_coalesced() { coalesced_ = true; }
   bool coalesced() const { return coalesced_; }
   int64_t trace_id() const { return trace_id_; }
+  void set_trace_id(int64_t trace_id) { trace_id_ = trace_id; }
 
  private:
   void AddLatencyNumberWithTimestampImpl(LatencyComponentType component,
@@ -235,6 +237,8 @@ class LatencyInfo {
   int64_t trace_id_;
   // Whether this event has been coalesced into another event.
   bool coalesced_;
+  // Whether a begin component has been added.
+  bool began_;
   // Whether a terminal component has been added.
   bool terminated_;
   // Stores the type of the first source event.