[Session restore] Add MRU logic to loading of background pages.

chrome/browser/ui/browser.cc

 // Copyright 2012 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/browser.h"
 
 #if defined(OS_WIN)
 #include <windows.h>
 #include <shellapi.h>
 #endif  // defined(OS_WIN)
@@ skipping 1053 matching lines @@
     // Show the loading state (if any).
     status_bubble->SetStatus(CoreTabHelper::FromWebContents(
         tab_strip_model_->GetActiveWebContents())->GetStatusText());
   }
 
   if (HasFindBarController()) {
     find_bar_controller_->ChangeWebContents(new_contents);
     find_bar_controller_->find_bar()->MoveWindowIfNecessary(gfx::Rect());
   }
 
-  // Update sessions. Don't force creation of sessions. If sessions doesn't
-  // exist, the change will be picked up by sessions when created.
+  // Update sessions (selected tab index and last activation time). Don't force
+  // creation of sessions. If sessions doesn't exist, the change will be picked
+  // up by sessions when created.
   SessionService* session_service =
       SessionServiceFactory::GetForProfileIfExisting(profile_);
   if (session_service && !tab_strip_model_->closing_all()) {
     session_service->SetSelectedTabInWindow(session_id(),
                                             tab_strip_model_->active_index());
+    SessionTabHelper* session_tab_helper =
+        SessionTabHelper::FromWebContents(new_contents);
+    session_service->SetActivationTime(

[sky, 2015/05/12 21:25:30]

I think you should only do this if the tab is active for long enough. For
example, if I rapidly control-tab between a bunch of tabs there is no point in
generating an id for each. If you didn't do this, then you could add the
activation time to SetSelectedTabInWindow.

[Georges Khalil, 2015/05/15 16:55:30]

The length if the activation is something that's going to be tackled in a
subsequent CL. For now, we're going with the simple method of recording all tab
switching but this will be improved soon.

Putting this in the experiment, as per previous comment.

[sky, 2015/05/22 03:00:19]

Can you outline where you're thinking you'll go with that? If we're always going
to update active time you could make SetSelectedTabInWindow take the time stamp
and not create another command.

[Georges Khalil, 2015/05/22 20:14:09]

Forgot to mention that we need to keep them separated because when
BuildCommandsFromBrowsers is called, it will only save one
SetSelectedTabInWindow per window, for the selected tab, whereas we need one per
tab, to save all the last active times.

As for the length of the activation, I haven't looked into it in detail, but my
first instinct would be to start a timer here for new_contents and stop the
timer of old_contents. And whenever the timer fires, enough time has elapsed and
save the time.

WDYT?

[sky, 2015/05/22 20:25:30]

We could change session restore to not only keep one around, but that is only
useful it we don't do something more interesting here. Sounds like we are going
to more interesting, which is good.
I think you'll end up needing to track this in sessionrestore too (or perhaps
set some userdata on the webcontents), but you can worry about that later.

+        session_id(), session_tab_helper->session_id(), base::TimeTicks::Now());
   }
 
   // This needs to be called after notifying SearchDelegate.
   if (instant_controller_)
     instant_controller_->ActiveTabChanged();
 
   autofill::ChromeAutofillClient::FromWebContents(new_contents)->TabActivated();
   SearchTabHelper::FromWebContents(new_contents)->OnTabActivated();
 }
 
@@ skipping 1512 matching lines @@
   if (contents && !allow_js_access) {
     contents->web_contents()->GetController().LoadURL(
         target_url,
         content::Referrer(),
         ui::PAGE_TRANSITION_LINK,
         std::string());  // No extra headers.
   }
 
   return contents != NULL;
 }