Introduce ActiveScriptController; track active extension scripts

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 faef4a334f99294754ad4d26e7ecd6fd05fbf0dc..5ba98a827b431842a85a559b0af6e50f91733ae7 100644
--- a/tools/metrics/histograms/histograms.xml
+++ b/tools/metrics/histograms/histograms.xml
@@ -5381,6 +5381,16 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="ExtensionActivity.AdInjectionCouldHaveBeenStopped"
+    units="Boolean">
+  <owner>kalman@chromium.org</owner>
+  <owner>rdevlin.cronin@chromium.org</owner>
+  <summary>
+    Whether or not a detected ad injection could have been stopped by asking the
+    user's permission before injecting an extension script.

[not at google - send to devlin, 2014/05/08 23:33:19]

I'll let isherman (or other) review this file properly, but it'd be worth
mentioning here the ActivityLog UMA which relates to this.

[Devlin, 2014/05/09 00:15:32]

Done.

+  </summary>
+</histogram>
+
 <histogram name="ExtensionActivity.AdRemoved" units="Extension Count">
   <owner>felt@chromium.org</owner>
   <owner>rdevlin.cronin@chromium.org</owner>
@@ -5725,6 +5735,16 @@ Therefore, the affected-histogram name has to have at least one dot in it.
   </summary>
 </histogram>
 
+<histogram name="Extensions.ActiveScriptController.ShownActiveScriptsOnPage"
+    units="Number of Actions">
+  <owner>kalman@chromium.org</owner>
+  <owner>rdevlin.cronin@chromium.org</owner>
+  <summary>
+    The number of extensions which would display an Active Script Running
+    indiciation to the user. Recorded at page close.
+  </summary>
+</histogram>
+
 <histogram name="Extensions.AllocatePortIdPairOverflow">
   <owner>Please list the metric's owners. Add more owner tags as needed.</owner>
   <summary>