Don't set ion=1 for hidden Instant modes.

chrome/browser/search_engines/search_terms_data.h

Index: chrome/browser/search_engines/search_terms_data.h
diff --git a/chrome/browser/search_engines/search_terms_data.h b/chrome/browser/search_engines/search_terms_data.h
index dd4468aa8c2e4011d21709d48616678ee59ce2e4..fc1fe09b432a52f48597308c32d5ac12a6e0e5ff 100644
--- a/chrome/browser/search_engines/search_terms_data.h
+++ b/chrome/browser/search_engines/search_terms_data.h
@@ -35,6 +35,14 @@ class SearchTermsData {
   virtual string16 GetRlzParameterValue() const = 0;
 #endif
 
+  // Returns a string indicating whether Instant (in the visible-preview mode)
+  // is enabled, suitable for adding as a query string param to the homepage
+  // (instant_url) request. Returns an empty string if Instant is disabled,
+  // or if it's only active in a hidden field trial mode. Determining this
+  // requires accessing the Profile, so this can only ever be non-empty for
+  // UIThreadSearchTermsData.
+  virtual std::string InstantEnabledParam() const;
+
   // Returns a string indicating the Instant field trial group, suitable for
   // adding as a query string param to suggest/search URLs, or an empty string
   // if the field trial is not active. Checking the field trial group requires
@@ -51,8 +59,8 @@ class UIThreadSearchTermsData : public SearchTermsData {
  public:
   UIThreadSearchTermsData();
 
-  // Callers who need an accurate answer from InstantFieldTrialUrlParam() must
-  // set the profile here before calling that.
+  // Callers who need an accurate answer from InstantFieldTrialUrlParam() or
+  // InstantEnabledParam() must set the profile here before calling them.
   void set_profile(Profile* profile) { profile_ = profile; }
 
   // Implementation of SearchTermsData.
@@ -64,6 +72,10 @@ class UIThreadSearchTermsData : public SearchTermsData {
 
   // This returns the empty string unless set_profile() has been called with a
   // non-NULL Profile.
+  virtual std::string InstantEnabledParam() const OVERRIDE;
+
+  // This returns the empty string unless set_profile() has been called with a
+  // non-NULL Profile.
   virtual std::string InstantFieldTrialUrlParam() const OVERRIDE;
 
   // Used by tests to set the value for the Google base url. This takes