[WillSplitBeforeLand] Add UMAs to measure how user interacts with tabs

chrome/browser/ui/tabs/tab_strip_model_stats_recorder.h

Index: chrome/browser/ui/tabs/tab_strip_model_stats_recorder.h
diff --git a/chrome/browser/ui/tabs/tab_strip_model_stats_recorder.h b/chrome/browser/ui/tabs/tab_strip_model_stats_recorder.h
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index 0000000000000000000000000000000000000000..9bd9ab0ab85b0fa996a05cd4d465f0cb1cb16789
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+++ b/chrome/browser/ui/tabs/tab_strip_model_stats_recorder.h
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+// 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.
+
+#ifndef CHROME_BROWSER_UI_TABS_TAB_STRIP_MODEL_STATS_RECORDER_H_
+#define CHROME_BROWSER_UI_TABS_TAB_STRIP_MODEL_STATS_RECORDER_H_
+
+#include <list>
+
+#include "base/containers/hash_tables.h"
+#include "base/time/time.h"
+#include "chrome/browser/ui/browser_list_observer.h"
+#include "chrome/browser/ui/tabs/tab_strip_model_observer.h"
+
+namespace content {
+class WebContents;
+}
+
+namespace chrome {
+
+// TabStripModelStatsRecorder records user tab interaction stats.
+// In particular, we record tab's lifetime and state transition probability to
+// study user interaction with background tabs. (crbug.com/517335)
+class TabStripModelStatsRecorder : public BrowserListObserver,
+                                   public TabStripModelObserver {
+ public:
+  TabStripModelStatsRecorder();
+  ~TabStripModelStatsRecorder() override;
+
+  // chrome::BrowserListObserver implementation.
+  void OnBrowserAdded(Browser* browser) override;
+  void OnBrowserRemoved(Browser* browser) override;
+  void OnBrowserSetLastActive(Browser* browser) override {}
+
+  // TabStripModelObserver implementation.
+  void TabInsertedAt(content::WebContents* contents,
+                     int index,
+                     bool foreground) override;
+  void TabClosingAt(TabStripModel* tab_strip_model,
+                    content::WebContents* contents,
+                    int index) override;
+  void TabDetachedAt(content::WebContents* contents, int index) override;
+  void ActiveTabChanged(content::WebContents* old_contents,
+                        content::WebContents* new_contents,
+                        int index,
+                        int reason) override;
+  void TabReplacedAt(TabStripModel* tab_strip_model,
+                     content::WebContents* old_contents,
+                     content::WebContents* new_contents,
+                     int index) override;
+
+  class TabInfo {
+   public:
+    enum class State {
+      INITIAL = 0,
+      ACTIVE,
+      INACTIVE,
+      DETACHED,
+      CLOSED,
+      MAX,
+    };
+
+    void UpdateState(State new_state);
+
+    State state() const { return current_state_; }
+
+   private:
+    State current_state_ = State::INITIAL;
+    base::Time last_state_modified_;
+  };
+
+ private:
+  base::hash_map<content::WebContents*, TabInfo> tab_info_map_;
+  int last_active_index_ = 0;
+  std::list<content::WebContents*> active_tab_history_;
+};
+
+}  // namespace chrome
+
+#endif  // CHROME_BROWSER_UI_TABS_TAB_STRIP_MODEL_STATS_RECORDER_H_