Add metrics to keep track of the tab activate/deactivate cycle

chrome/browser/metrics/tab_reactivation_tracker.cc

Index: chrome/browser/metrics/tab_reactivation_tracker.cc
diff --git a/chrome/browser/metrics/tab_reactivation_tracker.cc b/chrome/browser/metrics/tab_reactivation_tracker.cc
new file mode 100644
index 0000000000000000000000000000000000000000..c3127b13e9d60f841d248b95bf82ecda5024bb72
--- /dev/null
+++ b/chrome/browser/metrics/tab_reactivation_tracker.cc
@@ -0,0 +1,127 @@
+// Copyright 2016 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/metrics/tab_reactivation_tracker.h"
+
+#include "base/memory/ptr_util.h"
+#include "base/stl_util.h"
+#include "content/public/browser/web_contents_observer.h"
+
+namespace metrics {
+
+// This class is used to track the activation/deactivation cycle per
+// WebContents.
+class TabReactivationTracker::WebContentsHelper
+    : public content::WebContentsObserver {
+ public:
+  WebContentsHelper(TabReactivationTracker* tab_reactivation_tracker,
+                    content::WebContents* contents);
+  ~WebContentsHelper() override;
+
+  // content::WebContentsObserver:
+  void WebContentsDestroyed() override;
+
+  void OnTabActivating();
+  void OnTabDeactivating();
+  void OnTabClosing();
+
+ private:
+  // The owning TabReactivationTracker.
+  TabReactivationTracker* tab_reactivation_tracker_;
+
+  // Indicates if the tab has been deactivated before as to only count
+  // reactivations.
+  bool was_deactivated_once_;
+
+  // The deactivation metric is not recorded for closing tabs.
+  bool is_closing_;
+
+  DISALLOW_COPY_AND_ASSIGN(WebContentsHelper);
+};
+
+TabReactivationTracker::WebContentsHelper::WebContentsHelper(
+    TabReactivationTracker* tab_reactivation_tracker,
+    content::WebContents* contents)
+    : content::WebContentsObserver(contents),
+      tab_reactivation_tracker_(tab_reactivation_tracker),
+      was_deactivated_once_(false),
+      is_closing_(false) {}
+
+TabReactivationTracker::WebContentsHelper::~WebContentsHelper() = default;
+
+void TabReactivationTracker::WebContentsHelper::WebContentsDestroyed() {
+  tab_reactivation_tracker_->OnWebContentsDestroyed(web_contents());
+}
+
+void TabReactivationTracker::WebContentsHelper::OnTabActivating() {
+  if (was_deactivated_once_)
+    tab_reactivation_tracker_->NotifyTabReactivating(web_contents());
+}
+
+void TabReactivationTracker::WebContentsHelper::OnTabDeactivating() {
+  was_deactivated_once_ = true;
+  if (!is_closing_)
+    tab_reactivation_tracker_->NotifyTabDeactivating(web_contents());
+}
+
+void TabReactivationTracker::WebContentsHelper::OnTabClosing() {
+  is_closing_ = true;
+}
+
+TabReactivationTracker::TabReactivationTracker(Delegate* delegate)
+    : delegate_(delegate), browser_tab_strip_tracker_(this, nullptr, nullptr) {
+  browser_tab_strip_tracker_.Init(
+      BrowserTabStripTracker::InitWith::ALL_BROWERS);
+}
+
+TabReactivationTracker::~TabReactivationTracker() = default;
+
+void TabReactivationTracker::TabInsertedAt(TabStripModel* tab_strip_model,
+                                           content::WebContents* contents,
+                                           int index,
+                                           bool foreground) {}
+
+void TabReactivationTracker::TabClosingAt(TabStripModel* tab_strip_model,
+                                          content::WebContents* contents,
+                                          int index) {
+  GetHelper(contents)->OnTabClosing();
+}
+
+void TabReactivationTracker::ActiveTabChanged(
+    content::WebContents* old_contents,
+    content::WebContents* new_contents,
+    int index,
+    int reason) {
+  if (old_contents)
+    GetHelper(old_contents)->OnTabDeactivating();
+  GetHelper(new_contents)->OnTabActivating();
+}
+
+void TabReactivationTracker::NotifyTabDeactivating(
+    content::WebContents* contents) {
+  delegate_->OnTabDeactivated(contents);
+}
+
+void TabReactivationTracker::NotifyTabReactivating(
+    content::WebContents* contents) {
+  delegate_->OnTabReactivated(contents);
+}
+
+TabReactivationTracker::WebContentsHelper* TabReactivationTracker::GetHelper(
+    content::WebContents* contents) {
+  // Make sure it exists.
+  if (!base::ContainsKey(helper_map_, contents)) {
+    helper_map_.insert(std::make_pair(
+        contents, base::MakeUnique<WebContentsHelper>(this, contents)));
+  }
+
+  return helper_map_[contents].get();
+}
+
+void TabReactivationTracker::OnWebContentsDestroyed(
+    content::WebContents* contents) {
+  helper_map_.erase(contents);
+}
+
+}  // namespace metrics