Optional <TimeDelta> since they may be non existent.

components/page_load_metrics/common/page_load_timing.h

Index: components/page_load_metrics/common/page_load_timing.h
diff --git a/components/page_load_metrics/common/page_load_timing.h b/components/page_load_metrics/common/page_load_timing.h
index 285cf65aa3b946cf78d7c4ed430ca69ac6fcf65b..56b55efb5bd1b63ed14f2dd0fa117c605437dfdd 100644
--- a/components/page_load_metrics/common/page_load_timing.h
+++ b/components/page_load_metrics/common/page_load_timing.h
@@ -26,6 +26,13 @@ struct PageLoadTiming {
 
   // All TimeDeltas are relative to navigation_start
 
+  // @shivanisha TODO Issue 596367 shows that it is possible for a existent

[Bryan McQuade, 2016/03/29 18:33:43]

style nit:
TODO(shivanisha): Issue ...

[shivanisha, 2016/03/29 18:54:25]

updating the comment

+  // TimeDelta value to be 0 (2 TimeTicks can have the same value even if they
+  // were assigned in separate instructions if the clock speed is less
+  // granular). The solution there was to use base::Optional for those values.
+  // Consider changing the below values to Optional as well when serialization
+  // supports it.
+
   // Time that the first byte of the response is received.
   base::TimeDelta response_start;