[Extensions] Add metrics for UserScriptListener

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 e32dc38380278985d11dc2f22e52acd876372746..63ab70f48e98f6c793c2642defc50b30eb46083f 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -2064,17 +2064,18 @@ Therefore, the affected-histogram name has to have at least one dot in it.
 <histogram name="Autofill.UnmaskPrompt.Events" enum="AutofillUnmaskPromptEvent">
   <owner>waltercacau@chromium.org</owner>
   <summary>
-    Events tracking the usage of the unmasking prompt. This prompt is
-    triggered when a user selects a masked card in a autofill dropdown.
+    Events tracking the usage of the unmasking prompt. This prompt is triggered
+    when a user selects a masked card in a autofill dropdown.
   </summary>
 </histogram>
 
-<histogram name="Autofill.UnmaskPrompt.GetRealPanResult" enum="AutofillGetRealPanResult">
+<histogram name="Autofill.UnmaskPrompt.GetRealPanResult"
+    enum="AutofillGetRealPanResult">
   <owner>waltercacau@chromium.org</owner>
   <summary>
-    Tracks the result of the GetRealPan API call. This API call is triggered
-    by the unmasking prompt when the user types information to verify his
-    ownership of the card being fetched.
+    Tracks the result of the GetRealPan API call. This API call is triggered by
+    the unmasking prompt when the user types information to verify his ownership
+    of the card being fetched.
   </summary>
 </histogram>
 
@@ -9877,6 +9878,26 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Extensions.ThrottledNetworkRequestDelay" units="milliseconds">
+  <owner>rdevlin.cronin@chromium.org</owner>
+  <owner>kalman@chromium.org</owner>
+  <summary>
+    The duration by which a network request was delayed while waiting for
+    extension user script load. Recorded once per request that is delayed, at
+    the time the resource resumes loading.
+  </summary>
+</histogram>
+
+<histogram name="Extensions.ThrottledNetworkRequests" units="requests">
+  <owner>rdevlin.cronin@chromium.org</owner>
+  <owner>kalman@chromium.org</owner>
+  <summary>
+    The total number of network requests that were delayed by extension user
+    script load. Recorded once each time network requests may have been delayed
+    by user script load (i.e., once at the end of each batch of script loads).
+  </summary>
+</histogram>
+
 <histogram name="Extensions.ToolstripLoadTime" units="milliseconds">
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <summary>Time taken to load a toolstrip.</summary>