Move instant support to SearchTabHelper. Fix InstantTab reset.

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 53d0fcc9efd245bd685085d5c55051b98176cf6e..42cc4f9a896344ef372aaaf8fa541925d777ac7e 100644
--- a/chrome/browser/ui/search/search_model.cc
+++ b/chrome/browser/ui/search/search_model.cc
@@ -77,6 +77,24 @@ void SearchModel::SetTopBarsVisible(bool visible) {
                     ModelChanged(old_state, state_));
 }
 
+void SearchModel::SetSupportsInstant(bool supports_instant) {
+  DCHECK(chrome::IsInstantExtendedAPIEnabled())
+      << "Please do not try to set the SearchModel mode without first "
+      << "checking if Search is enabled.";
+
+  InstantSupportState new_instant_support = supports_instant ?
+      INSTANT_SUPPORT_YES : INSTANT_SUPPORT_NO;
+
+  if (state_.instant_support == new_instant_support)
+    return;
+
+  const State old_state = state_;
+  state_.instant_support = new_instant_support;
+
+  FOR_EACH_OBSERVER(SearchModelObserver, observers_,
+                    ModelChanged(old_state, state_));
+}
+
 void SearchModel::AddObserver(SearchModelObserver* observer) {
   observers_.AddObserver(observer);
 }