[Extensions] Add coarse metrics for extension function performance

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 2f8df067687647edf40dbeec32e4f83d2dddac51..4ce19ed855c1265ff1ca5c72c928675b9c5aba51 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -13589,6 +13589,37 @@ http://cs/file:chrome/histograms.xml - but prefer this file for new entries.
   <summary>Number of calls to extension functions.</summary>
 </histogram>
 
+<histogram name="Extensions.Functions.FailedTotalExecutionTime" units="ms">
+  <owner>rdevlin.cronin@chromium.org</owner>
+  <summary>
+    The total amount of time it took to execute an extension function that
+    failed from the time the extension function is called to the time the
+    function responds. Note that since some extension functions are inherently
+    slow (anything that requires user interaction, for instance), this is not a
+    definitive source for function performance.
+  </summary>
+</histogram>
+
+<histogram name="Extensions.Functions.SucceededTotalExecutionTime" units="ms">
+  <owner>rdevlin.cronin@chromium.org</owner>
+  <summary>
+    The total amount of time it took to execute an extension function that
+    succeeded from the time the extension function is called to the time the
+    function responds. Note that since some extension functions are inherently
+    slow (anything that requires user interaction, for instance), this is not a
+    definitive source for function performance.
+  </summary>
+</histogram>
+
+<histogram name="Extensions.Functions.SynchronousExecutionTime" units="ms">
+  <owner>rdevlin.cronin@chromium.org</owner>
+  <summary>
+    The synchronous amount of time an extension function takes. Note that many
+    extension functions run asynchronously; see also
+    Extensions.Functions.[Succeeded|Failed]TotalExecutionTime.
+  </summary>
+</histogram>
+
 <histogram name="Extensions.GetUserDataTempDir" enum="GetUserDataTempDirResult">
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <summary>