Bug 1275570 - "Add Telemetry probe to see how often users enter print preview, and how many simplify the view". r=mconley

toolkit/components/printing/content/printUtils.js

@@ -197,6 +197,9 @@ var PrintUtils = {
       this._sourceBrowser = aListenerObj.getSourceBrowser();
       this._originalTitle = this._sourceBrowser.contentTitle;
       this._originalURL = this._sourceBrowser.currentURI.spec;
+
+      // Here we log telemetry data for when the user enters print preview.
+      this.logTelemetry("PRINT_PREVIEW_OPENED_COUNT");
     } else {
       // collapse the browser here -- it will be shown in
       // enterPrintPreview; this forces a reflow which fixes display
@@ -530,6 +533,9 @@ var PrintUtils = {
           URL: this._listener.getSourceBrowser().currentURI.spec,
           windowID: this._listener.getSourceBrowser().outerWindowID,
         });
+
+        // Here we log telemetry data for when the user enters simplify mode.
+        this.logTelemetry("PRINT_PREVIEW_SIMPLIFY_PAGE_OPENED_COUNT");
       }
     } else {
       sendEnterPreviewMessage(this._listener.getSourceBrowser(), false);
@@ -635,6 +641,12 @@ var PrintUtils = {
     this._listener.onExit();
   },
 
+  logTelemetry: function (ID)
+  {
+    let histogram = Services.telemetry.getHistogramById(ID);
+    histogram.add(true);
+  },
+
   onKeyDownPP: function (aEvent)
   {
     // Esc exits the PP

toolkit/components/telemetry/Histograms.json

@@ -5879,6 +5879,22 @@
     "n_buckets": 50,
     "description": "(Bug 1207089) Time in ms between displaying a popup notification and dismissing it without an action the first time, keyed by ID"
   },
+  "PRINT_PREVIEW_OPENED_COUNT": {
+    "alert_emails": ["carnold@mozilla.org"],
+    "bug_numbers": [1275570],
+    "expires_in_version": "56",
+    "kind": "count",
+    "releaseChannelCollection": "opt-out",
+    "description": "A counter incremented every time the browser enters print preview."
+  },
+  "PRINT_PREVIEW_SIMPLIFY_PAGE_OPENED_COUNT": {
+    "alert_emails": ["carnold@mozilla.org"],
+    "bug_numbers": [1275570],
+    "expires_in_version": "56",
+    "kind": "count",
+    "releaseChannelCollection": "opt-out",
+    "description": "A counter incremented every time the browser enters simplified mode on print preview."
+  },
   "DEVTOOLS_DEBUGGER_RDP_LOCAL_RELOAD_MS": {
     "expires_in_version": "never",
     "kind": "exponential",