Add UMA histogram to track the various sources that request the feedback app

chrome/browser/supervised_user/supervised_user_interstitial.cc

Index: chrome/browser/supervised_user/supervised_user_interstitial.cc
diff --git a/chrome/browser/supervised_user/supervised_user_interstitial.cc b/chrome/browser/supervised_user/supervised_user_interstitial.cc
index 1671a75023230989291dad04121b3c248236eb3a..b81ac22c6781620cf18d40fab84d508432e8d629 100644
--- a/chrome/browser/supervised_user/supervised_user_interstitial.cc
+++ b/chrome/browser/supervised_user/supervised_user_interstitial.cc
@@ -271,7 +271,8 @@ void SupervisedUserInterstitial::CommandReceived(const std::string& command) {
     ReportChildAccountFeedback(web_contents_, message, url_);
 #else
     chrome::ShowFeedbackPage(chrome::FindBrowserWithWebContents(web_contents_),
-                             message, std::string());
+                             chrome::kFeedbackSourceSupervisedUserInterstitial,
+                             message, std::string() /* category_tag */);
 #endif
     return;
   }