[Remote suggestions] Report time distribution of triggers

tools/metrics/histograms/histograms.xml

Index: tools/metrics/histograms/histograms.xml
diff --git a/tools/metrics/histograms/histograms.xml b/tools/metrics/histograms/histograms.xml
index c11089e05d692f90906ee3048e51e2229d74b7b9..cc1321acff22022acfc3292b74a1d5f61c4351aa 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -41668,6 +41668,30 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram name="NewTabPage.ContentSuggestions.TimeUntilFirstSuccessfulTrigger"
+    units="ms">
+  <owner>jkrcal@chromium.org</owner>
+  <summary>
+    Android: The time difference between the last fetch and the first successful
+    fetch trigger. A successful trigger means that it came late enough, after
+    the respective scheduling interval elapsed. This is used to understand what
+    are the real fetching intervals in the wild.
+  </summary>
+</histogram>
+
+<histogram name="NewTabPage.ContentSuggestions.TimeUntilFirstTrigger"
+    units="ms">
+  <owner>jkrcal@chromium.org</owner>
+  <summary>
+    Android: The time difference between the last fetch and the first fetch
+    trigger. The first trigger may come before the respective scheduling
+    interval elapses, or after this moment. This metric is recorded once per
+    each soft fetch (per lifetime of a Chrome instance). This is used to
+    understand how changing scheduling intervals will impact traffic of
+    background fetches.
+  </summary>
+</histogram>
+
 <histogram name="NewTabPage.ContentSuggestions.UIUpdateResult"
     enum="ContentSuggestionsUIUpdateResult">
   <obsolete>
@@ -125340,6 +125364,16 @@ from previous Chrome versions.
   <affected-histogram name="Setup.Install.LzmaUnPackStatus"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="UserClasses">
+  <suffix name="RareNTPUser" label="Rare NTP user"/>
+  <suffix name="ActiveNTPUser" label="Active NTP user"/>
+  <suffix name="ActiveSuggestionsConsumer" label="Active suggestions consumer"/>
+  <affected-histogram
+      name="NewTabPage.ContentSuggestions.TimeUntilFirstSuccessfulTrigger"/>
+  <affected-histogram
+      name="NewTabPage.ContentSuggestions.TimeUntilFirstTrigger"/>
+</histogram_suffixes>
+
 <histogram_suffixes name="UserScriptRunLocation" separator=".">
   <suffix name="DocumentStart" label="Scripts with run_at: document_start."/>
   <suffix name="DocumentEnd" label="Scripts with run_at: document_end."/>