alternate ntp: implement Show/HideBars API to reduce jank when showing/hiding bars

chrome/browser/ui/search/search_model.h

Index: chrome/browser/ui/search/search_model.h
diff --git a/chrome/browser/ui/search/search_model.h b/chrome/browser/ui/search/search_model.h
index 6a7f1f138742d451a740290f5e5cc7a4c82b295a..f29308dff6e71b7879d76431a5d26405dcd5f9a2 100644
--- a/chrome/browser/ui/search/search_model.h
+++ b/chrome/browser/ui/search/search_model.h
@@ -21,13 +21,19 @@ class SearchModel {
   SearchModel();
   ~SearchModel();
 
-  // Change the mode.  Change notifications are sent to observers.  An animated
-  // transition may be requested.
+  // Change the mode.  Change notifications are sent to observers.
   void SetMode(const Mode& mode);
 
   // Get the active mode.
   const Mode& mode() const { return mode_; }
 
+  // Set visibility of top bars (bookmark and info bars).  Notifications are
+  // sent to observers.
+  void SetTopBarsVisible(bool visible);
+
+  // Get the visibility of top bars (bookmark and info bars).
+  bool top_bars_visible() const { return top_bars_visible_; }
+
   // Add and remove observers.
   void AddObserver(SearchModelObserver* observer);
   void RemoveObserver(SearchModelObserver* observer);
@@ -36,6 +42,9 @@ class SearchModel {
   // The display mode of UI elements such as the toolbar, the tab strip, etc.

[dhollowa, 2013/03/13 17:21:55]

For cleanliness, let's stick this model data into a struct, like:

 public:
  struct State {
    Mode mode;
    bool top_bars_visible;
  }
 private:
  State state_;

then in SMO...

 virtual void ModelChanged(
    const SearchModel::State& old_state,
    const SearchModel::State& new_state) = 0;

[kuan, 2013/03/13 22:21:07]

Done.

   Mode mode_;
 
+  // The visibility of top bars (bookmark and info bars).
+  bool top_bars_visible_;
+
   // Observers.
   ObserverList<SearchModelObserver> observers_;