Report page load timing information for child frames.

tools/metrics/histograms/enums.xml

Index: tools/metrics/histograms/enums.xml
diff --git a/tools/metrics/histograms/enums.xml b/tools/metrics/histograms/enums.xml
index c8a6a73f7562ff63de67b5ec88e21fe569e74eef..0eb13d53bf801928b4e550de298883a7baed0972 100644
--- a/tools/metrics/histograms/enums.xml
+++ b/tools/metrics/histograms/enums.xml
@@ -19463,10 +19463,12 @@ uploading your change for review.  These are checked by presubmit scripts.
   <int value="8" label="Inter process TimeTicks skew"/>
   <int value="9" label="No commit or failed provisional load received"/>
   <int value="10" label="No page load end time recorded"/>
-  <int value="11" label="Timing IPC received from subframe"/>
+  <int value="11" label="Timing IPC received from subframe (deprecated)"/>
   <int value="12" label="Invalid timing IPC (invalid timing descendent)"/>
   <int value="13" label="Invalid timing IPC (invalid behavior descendent)"/>
   <int value="14" label="Invalid timing IPC (invalid timing)"/>
+  <int value="15"
+      label="Subframe navigation start before main frame navigation start"/>
 </enum>
 
 <enum name="InterruptReason" type="int">