diff -r 000000000000 -r 6474c204b198 browser/components/tabview/telemetry.js
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/browser/components/tabview/telemetry.js	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,63 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this file,
+ * You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+/**
+ * Collects telemetry data for Tabview.
+ */
+let Telemetry = {
+  TOPIC_GATHER_TELEMETRY: "gather-telemetry",
+
+  /**
+   * Initializes the object.
+   */
+  init: function Telemetry_init() {
+    Services.obs.addObserver(this, this.TOPIC_GATHER_TELEMETRY, false);
+  }, 
+
+  /**
+   * Uninitializes the object.
+   */
+  uninit: function Telemetry_uninit() {
+    Services.obs.removeObserver(this, this.TOPIC_GATHER_TELEMETRY);
+  },
+
+  /**
+   * Adds telemetry values to gather usage statistics.
+   */
+  _collect: function Telemetry_collect() {
+    let stackedGroupsCount = 0;
+    let childCounts = [];
+
+    GroupItems.groupItems.forEach(function (groupItem) {
+      if (!groupItem.isEmpty()) {
+        childCounts.push(groupItem.getChildren().length);
+
+        if (groupItem.isStacked())
+          stackedGroupsCount++;
+      }
+    });
+
+    function addTelemetryValue(aId, aValue) {
+      Services.telemetry.getHistogramById("PANORAMA_" + aId).add(aValue);
+    }
+    function median(aChildCounts) {
+      aChildCounts.sort(function(x, y) { return x - y; });
+      let middle = Math.floor(aChildCounts.length / 2);
+      return aChildCounts[middle];
+    }
+
+    addTelemetryValue("GROUPS_COUNT", GroupItems.groupItems.length);
+    addTelemetryValue("STACKED_GROUPS_COUNT", stackedGroupsCount);
+    addTelemetryValue("MEDIAN_TABS_IN_GROUPS_COUNT", median(childCounts));
+  },
+
+  /**
+   * Observes for gather telemetry topic.
+   */
+  observe: function Telemetry_observe(aSubject, aTopic, aData) {
+    if (!gWindow.PrivateBrowsingUtils.isWindowPrivate(gWindow))
+      this._collect();
+  }
+}
+