Changes to default apps promo per ui leads:

chrome/browser/dom_ui/shown_sections_handler.h

 // Copyright (c) 2010 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_DOM_UI_SHOWN_SECTIONS_HANDLER_H_
 #define CHROME_BROWSER_DOM_UI_SHOWN_SECTIONS_HANDLER_H_
 #pragma once
 
 #include "chrome/browser/dom_ui/dom_ui.h"
 #include "chrome/common/notification_observer.h"
 #include "chrome/browser/prefs/pref_change_registrar.h"
 
 class DOMUI;
 class Extension;
 class Value;
 class PrefService;
 
 // Use for the shown sections bitmask.
 // Currently, only the THUMB and APPS sections can be toggled by the user. Other
 // sections are shown automatically if they have data, and hidden otherwise.
 enum Section {
   // If one of these is set, the corresponding section shows large thumbnails,
   // else it shows only a small overview list.
   THUMB = 1 << 0,

[Erik does not do reviews, 2011/01/10 16:48:57]

THUMB is a weird name for most visited.  this threw me at first.  might be worth
changing.

[Aaron Boodman, 2011/01/10 19:36:19]

Would require changing lots of JS too to match. I think it's out of scope for
this change.

   APPS = 1 << 6,
 
   // We use the low 16 bits for sections, the high 16 bits for minimized state.
   ALL_SECTIONS_MASK = 0x0000FFFF,
 
   // If one of these is set, then the corresponding section is shown minimized
   // at the bottom of the NTP and no data is directly visible on the NTP.
   MINIMIZED_THUMB = 1 << (0 + 16),
   MINIMIZED_RECENT = 1 << (2 + 16),
   MINIMIZED_APPS = 1 << (6 + 16),
 };
 
 class ShownSectionsHandler : public DOMMessageHandler,
                              public NotificationObserver {
  public:
   explicit ShownSectionsHandler(PrefService* pref_service);
   virtual ~ShownSectionsHandler() {}
 
   // Helper to get the current shown sections.
   static int GetShownSections(PrefService* pref_service);
 
+  // Expands |section|, collapsing any previously expanded section. This is the
+  // same thing that happens if a user clicks on |section|.
+  static void SetShownSection(PrefService* prefs, Section section);
+
   // DOMMessageHandler implementation.
   virtual void RegisterMessages();
 
   // NotificationObserver implementation.
   virtual void Observe(NotificationType type,
                        const NotificationSource& source,
                        const NotificationDetails& details);
 
   // Callback for "getShownSections" message.
   void HandleGetShownSections(const ListValue* args);
@@ skipping 11 matching lines @@
                                    const Extension* extension);
 
  private:
   PrefService* pref_service_;
   PrefChangeRegistrar pref_registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(ShownSectionsHandler);
 };
 
 #endif  // CHROME_BROWSER_DOM_UI_SHOWN_SECTIONS_HANDLER_H_