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

chrome/browser/ui/search/search_model.cc

Index: chrome/browser/ui/search/search_model.cc
diff --git a/chrome/browser/ui/search/search_model.cc b/chrome/browser/ui/search/search_model.cc
index 74232f32e8579f2b0181d03a1ee4b441c8b47d4c..5b5ab0d493caddeb3e0fc5bef5e93e53e69bdb53 100644
--- a/chrome/browser/ui/search/search_model.cc
+++ b/chrome/browser/ui/search/search_model.cc
@@ -10,7 +10,7 @@
 namespace chrome {
 namespace search {
 
-SearchModel::SearchModel() {
+SearchModel::SearchModel() : top_bars_visible_(true) {
 }
 
 SearchModel::~SearchModel() {
@@ -27,8 +27,25 @@ void SearchModel::SetMode(const Mode& new_mode) {
   const Mode old_mode = mode_;
   mode_ = new_mode;
 
+  // For |SEARCH_SUGGESTIONS| and |SEARCH_RESULTS| modes, SearchBox API will
+  // determine visibility of top bars via SetTopBarsVisible(); for other modes,
+  // top bars are always visible, if available.
+  if (!mode_.is_search())
+    top_bars_visible_ = true;
+
+  FOR_EACH_OBSERVER(SearchModelObserver, observers_,
+                    ModelChanged(old_mode, mode_, top_bars_visible_));
+}
+
+void SearchModel::SetTopBarsVisible(bool visible) {
+  DCHECK(IsInstantExtendedAPIEnabled())
+      << "Please do not try to set the SearchModel mode without first "
+      << "checking if Search is enabled.";
+
+  top_bars_visible_ = visible;

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

Do an early return if there's no change to the visibility.

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

Done.

+

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

Save off old_state_  here so the receiver can determine what changed.  i.e.:

  FOE(..., ModelChanged(old_state, state_));

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

Done.

   FOR_EACH_OBSERVER(SearchModelObserver, observers_,
-                    ModeChanged(old_mode, mode_));
+                    ModelChanged(mode_, mode_, top_bars_visible_));
 }
 
 void SearchModel::AddObserver(SearchModelObserver* observer) {