Add a URL param to indicate group selection in Instant field trial.

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 a695a113c7eca0c3c50913ef03895142f98e1622..ec108014efa3b6fdf016e76ac513460fd660c874 100644
--- a/chrome/browser/search_engines/search_terms_data.h
+++ b/chrome/browser/search_engines/search_terms_data.h
@@ -11,6 +11,8 @@
 #include "base/basictypes.h"
 #include "base/string16.h"
 
+class Profile;
+
 // All data needed by TemplateURLRef::ReplaceSearchTerms which typically may
 // only be accessed on the UI thread.
 class SearchTermsData {
@@ -32,6 +34,13 @@ class SearchTermsData {
   virtual string16 GetRlzParameterValue() const = 0;
 #endif
 
+  // 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
+  // accessing the Profile, which means this can only ever be non-empty for
+  // UIThreadSearchTermsData.
+  virtual std::string InstantFieldTrialUrlParam() const;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(SearchTermsData);
 };
@@ -41,6 +50,10 @@ class UIThreadSearchTermsData : public SearchTermsData {
  public:
   UIThreadSearchTermsData();
 
+  // Callers who need an accurate answer from InstantFieldTrialUrlParam() must
+  // set the profile here before calling that.
+  void set_profile(Profile* profile) { profile_ = profile; }
+
   // Implementation of SearchTermsData.
   virtual std::string GoogleBaseURLValue() const;
   virtual std::string GetApplicationLocale() const;
@@ -48,12 +61,17 @@ class UIThreadSearchTermsData : public SearchTermsData {
   virtual string16 GetRlzParameterValue() const;
 #endif
 
+  // This returns the empty string unless set_profile() has been called with a
+  // non-NULL Profile.
+  virtual std::string InstantFieldTrialUrlParam() const;
+
   // Used by tests to set the value for the Google base url. This takes
   // ownership of the given std::string.
   static void SetGoogleBaseURL(std::string* google_base_url);
 
  private:
   static std::string* google_base_url_;
+  Profile* profile_;
 
   DISALLOW_COPY_AND_ASSIGN(UIThreadSearchTermsData);
 };