[Tab Metrics] Added TabManager.SessionRestore.SwitchToTab UMA.

chrome/browser/resource_coordinator/tab_manager_web_contents_data.h

 // 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_RESOURCE_COORDINATOR_TAB_MANAGER_WEB_CONTENTS_DATA_H_
 #define CHROME_BROWSER_RESOURCE_COORDINATOR_TAB_MANAGER_WEB_CONTENTS_DATA_H_
 
 #include "base/macros.h"
 #include "base/time/time.h"
 #include "chrome/browser/resource_coordinator/tab_manager.h"
@@ skipping 11 matching lines @@
 
 namespace resource_coordinator {
 
 // Tabs (WebContentsData) start in the not loading state, and transition to the
 // loading state when a navigation begins in the main frame of the associated
 // WebContents. The state changes to loaded when we receive the DidStopLoading*
 // signal. The state can change from loaded to loading if another navigation
 // occurs in the main frame, which happens if the user navigates to a new page
 // and the WebContents is reused.
 //
+// These values are used in the TabManager.SessionRestore.SwitchToTab UMA.
+//
+// TODO(shaseley): Add a reference to the new metric when background tab loading
+// is done.
+//
 // TODO(shaseley): *switch to the new done signal (network and cpu quiescence)
 // when available.
-//
-// TODO(shaseley): This will become an UMA histogram once the TabManager is
-// aware of session restore begin/end and background tab loading begin/end.
 enum TabLoadingState {
   TAB_IS_NOT_LOADING = 0,

[lpy, 2017/06/27 22:30:36]

I think that TAB_IS_NOT_LOADING is not accurate, a tab can be loaded and is not
loading.

We can do it in a separate patch.

[shaseley, 2017/06/27 23:22:10]

I know what you mean, the names are a little confusing in that regard. This enum
mirrors the one used in session restore for the same purpose, so I kept the
names the same erring on the side of consistency.

   TAB_IS_LOADING = 1,
   TAB_IS_LOADED = 2,
   TAB_LOADING_STATE_MAX,
 };
 
 // Internal class used by TabManager to record the needed data for
 // WebContentses.
 class TabManager::WebContentsData
     : public content::WebContentsObserver,
       public content::WebContentsUserData<TabManager::WebContentsData> {
@@ skipping 73 matching lines @@
 
   // Returns the TabLoadingState of the tab.
   TabLoadingState tab_loading_state() const {
     return tab_data_.tab_loading_state;
   }
 
  private:
   // Needed to access tab_data_.
   FRIEND_TEST_ALL_PREFIXES(TabManagerWebContentsDataTest, CopyState);
   FRIEND_TEST_ALL_PREFIXES(TabManagerWebContentsDataTest, TabLoadingState);
+  FRIEND_TEST_ALL_PREFIXES(TabManagerTest, HistogramsSessionRestoreSwitchToTab);
 
   struct Data {
     Data();
     bool operator==(const Data& right) const;
     bool operator!=(const Data& right) const;
 
     // Is the tab currently discarded?
     bool is_discarded;
     // Number of times the tab has been discarded.
     int discard_count;
@@ skipping 37 matching lines @@
 
   // True if the tab has been purged.
   bool is_purged_;
 
   DISALLOW_COPY_AND_ASSIGN(WebContentsData);
 };
 
 }  // namespace resource_coordinator
 
 #endif  // CHROME_BROWSER_RESOURCE_COORDINATOR_TAB_MANAGER_WEB_CONTENTS_DATA_H_