Update from https://crrev.com/316786

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 95cf06d5a576c061eda861c74f923de6c50b9eef..9ca0ddc3b6075bf78e7818a5ae2038742cb27e43 100644
--- a/base/trace_event/trace_event_impl.cc
+++ b/base/trace_event/trace_event_impl.cc
@@ -1908,11 +1908,13 @@ TraceEventHandle TraceLog::AddTraceEventWithThreadIdAndTimestamp(
   AutoThreadLocalBoolean thread_is_in_trace_event(&thread_is_in_trace_event_);
 
   DCHECK(name);
+  DCHECK(!timestamp.is_null());
 
   if (flags & TRACE_EVENT_FLAG_MANGLE_ID)
     id ^= process_id_hash_;
 
-  TimeTicks now = OffsetTimestamp(timestamp);
+  TimeTicks offset_event_timestamp = OffsetTimestamp(timestamp);
+  TimeTicks now = OffsetNow();
   TimeTicks thread_now = ThreadNow();
 
   ThreadLocalEventBuffer* thread_local_event_buffer = NULL;
@@ -1985,8 +1987,8 @@ TraceEventHandle TraceLog::AddTraceEventWithThreadIdAndTimestamp(
     }
 
     if (trace_event) {
-      trace_event->Initialize(thread_id, now, thread_now, phase,
-                              category_group_enabled, name, id,
+      trace_event->Initialize(thread_id, offset_event_timestamp, thread_now,
+                              phase, category_group_enabled, name, id,
                               num_args, arg_names, arg_types, arg_values,
                               convertable_values, flags);
 
@@ -2024,7 +2026,7 @@ TraceEventHandle TraceLog::AddTraceEventWithThreadIdAndTimestamp(
     EventCallback event_callback = reinterpret_cast<EventCallback>(
         subtle::NoBarrier_Load(&event_callback_));
     if (event_callback) {
-      event_callback(now,
+      event_callback(offset_event_timestamp,
                      phase == TRACE_EVENT_PHASE_COMPLETE ?
                          TRACE_EVENT_PHASE_BEGIN : phase,
                      category_group_enabled, name, id,
@@ -2033,6 +2035,9 @@ TraceEventHandle TraceLog::AddTraceEventWithThreadIdAndTimestamp(
     }
   }
 
+  // Use |now| instead of |offset_event_timestamp| to compute overhead, because
+  // event timestamp may be not the real time that we started to add the event
+  // (e.g. event with zero timestamp or that was generated some time ago).
   if (thread_local_event_buffer)
     thread_local_event_buffer->ReportOverhead(now, thread_now);