Add UseCounters for alert(), confirm() and prompt() usage against site engagement.

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 5b988879ed8d2418545227de21e627142dff0c24..25f83c432706e43d7d4a820d64c9d07e27af4404 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -88326,6 +88326,24 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <int value="1728" label="NavigatorVibrateEngagementMedium"/>
   <int value="1729" label="NavigatorVibrateEngagementHigh"/>
   <int value="1730" label="NavigatorVibrateEngagementMax"/>
+  <int value="1731" label="AlertEngagementNone"/>
+  <int value="1732" label="AlertEngagementMinimal"/>
+  <int value="1733" label="AlertEngagementLow"/>
+  <int value="1734" label="AlertEngagementMedium"/>
+  <int value="1735" label="AlertEngagementHigh"/>
+  <int value="1736" label="AlertEngagementMax"/>
+  <int value="1737" label="ConfirmEngagementNone"/>
+  <int value="1738" label="ConfirmEngagementMinimal"/>
+  <int value="1739" label="ConfirmEngagementLow"/>
+  <int value="1740" label="ConfirmEngagementMedium"/>
+  <int value="1741" label="ConfirmEngagementHigh"/>
+  <int value="1742" label="ConfirmEngagementMax"/>
+  <int value="1743" label="PromptEngagementNone"/>
+  <int value="1744" label="PromptEngagementMinimal"/>
+  <int value="1745" label="PromptEngagementLow"/>
+  <int value="1746" label="PromptEngagementMedium"/>
+  <int value="1747" label="PromptEngagementHigh"/>
+  <int value="1748" label="PromptEngagementMax"/>
 </enum>
 
 <enum name="FetchRequestMode" type="int">