[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 18ad474ad9b6740d66d9e28df345bcade93ab07f..fd8d5a386e6d6db609872e06f5c58b9c95c34d1c 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -41736,6 +41736,38 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   </summary>
 </histogram>
 
+<histogram base="true"
+    name="NewTabPage.ContentSuggestions.TimeUntilFirstSoftTrigger" units="ms">
+  <owner>jkrcal@chromium.org</owner>
+  <summary>
+    Android: The time since the last fetch, recorded upon the first soft fetch
+    trigger. The first soft trigger does not necessarily cause a fetch (if it
+    comes before the end of the respective scheduling interval). This metric is
+    recorded at most once (per lifetime of a Chrome instance) after each fetch.
+    This is used to understand how changing scheduling intervals will impact
+    traffic of background fetches.
+  </summary>
+</histogram>
+
+<histogram base="true"
+    name="NewTabPage.ContentSuggestions.TimeUntilPersistentFetch" units="ms">
+  <owner>jkrcal@chromium.org</owner>
+  <summary>
+    Android: The time since the last fetch, recorded upon a persistent fetch.
+    This is used to understand what are the real persistent fetching intervals
+    in the wild.
+  </summary>
+</histogram>
+
+<histogram base="true" name="NewTabPage.ContentSuggestions.TimeUntilSoftFetch"
+    units="ms">
+  <owner>jkrcal@chromium.org</owner>
+  <summary>
+    Android: The time since the last fetch, recorded upon a soft fetch. This is
+    used to understand what are the real soft fetching intervals in the wild.
+  </summary>
+</histogram>
+
 <histogram name="NewTabPage.ContentSuggestions.UIUpdateResult"
     enum="ContentSuggestionsUIUpdateResult">
   <obsolete>
@@ -125435,6 +125467,17 @@ from previous Chrome versions.
   <affected-histogram name="Setup.Install.LzmaUnPackStatus"/>
 </histogram_suffixes>
 
+<histogram_suffixes name="UserClasses" separator=".">
+  <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.TimeUntilFirstSoftTrigger"/>
+  <affected-histogram
+      name="NewTabPage.ContentSuggestions.TimeUntilPersistentFetch"/>
+  <affected-histogram name="NewTabPage.ContentSuggestions.TimeUntilSoftFetch"/>
+</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."/>