Introduce TabStripModelStatsRecorder class to record tab interaction stats

chrome/browser/ui/tabs/tab_strip_model_stats_recorder.cc

Index: chrome/browser/ui/tabs/tab_strip_model_stats_recorder.cc
diff --git a/chrome/browser/ui/tabs/tab_strip_model_stats_recorder.cc b/chrome/browser/ui/tabs/tab_strip_model_stats_recorder.cc
new file mode 100644
index 0000000000000000000000000000000000000000..63ff347b617e6f8a0454872392fc78caf48d4e59
--- /dev/null
+++ b/chrome/browser/ui/tabs/tab_strip_model_stats_recorder.cc
@@ -0,0 +1,31 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#include "chrome/browser/ui/tabs/tab_strip_model_stats_recorder.h"
+
+#include <utility>
+
+#include "chrome/browser/ui/browser.h"
+#include "chrome/browser/ui/browser_iterator.h"
+#include "chrome/browser/ui/browser_list.h"
+#include "chrome/browser/ui/tabs/tab_strip_model.h"
+
+TabStripModelStatsRecorder::TabStripModelStatsRecorder() {
+  BrowserList::AddObserver(this);
+}
+
+TabStripModelStatsRecorder::~TabStripModelStatsRecorder() {
+  for (chrome::BrowserIterator iterator; !iterator.done(); iterator.Next())
+    iterator->tab_strip_model()->RemoveObserver(this);
+
+  BrowserList::RemoveObserver(this);
+}
+
+void TabStripModelStatsRecorder::OnBrowserAdded(Browser* browser) {
+  browser->tab_strip_model()->AddObserver(this);
+}
+
+void TabStripModelStatsRecorder::OnBrowserRemoved(Browser* browser) {
+  browser->tab_strip_model()->RemoveObserver(this);
+}