Bug 723515 - Add telemetry probe for the opening time of the Firefox app menu. r=ttaubert

browser/base/content/browser.js

@@ -1766,6 +1766,23 @@ function delayedStartup(isLoadingBlank, mustLoadSidebar) {
     document.getElementById("appmenu_charsetMenu").hidden = true;
 #endif
 
+  let appMenuButton = document.getElementById("appmenu-button");
+  let appMenuPopup = document.getElementById("appmenu-popup");
+  if (appMenuButton && appMenuPopup) {
+    let appMenuOpening = null;
+    appMenuButton.addEventListener("mousedown", function(event) {
+      if (event.button == 0)
+        appMenuOpening = new Date();
+    }, false);
+    appMenuPopup.addEventListener("popupshown", function(event) {
+      if (event.target != appMenuPopup || !appMenuOpening)
+        return;
+      let duration = new Date() - appMenuOpening;
+      appMenuOpening = null;
+      Services.telemetry.getHistogramById("FX_APP_MENU_OPEN_MS").add(duration);
+    }, false);
+  }
+
   window.addEventListener("mousemove", MousePosTracker, false);
   window.addEventListener("dragover", MousePosTracker, false);
 

toolkit/components/telemetry/TelemetryHistograms.h

@@ -313,6 +313,7 @@ HISTOGRAM(FX_TAB_ANIM_OPEN_MS, 1, 3000, 10, EXPONENTIAL, "Firefox: Time taken by
 HISTOGRAM(FX_TAB_ANIM_CLOSE_MS, 1, 3000, 10, EXPONENTIAL, "Firefox: Time taken by the tab closing animation in milliseconds")
 HISTOGRAM_BOOLEAN(FX_CONTEXT_SEARCH_AND_TAB_SELECT, "Firefox: Background tab was selected within 5 seconds of searching from the context menu")
 HISTOGRAM(FX_IDENTITY_POPUP_OPEN_MS, 1, 1000, 10, EXPONENTIAL, "Firefox: Time taken by the identity popup to open in milliseconds")
+HISTOGRAM(FX_APP_MENU_OPEN_MS, 1, 1000, 10, EXPONENTIAL, "Firefox: Time taken by the app-menu opening in milliseconds")
 
 /**
  * Thumbnail Service telemetry.