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

chrome/browser/search_engines/search_terms_data.h

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef CHROME_BROWSER_SEARCH_ENGINES_SEARCH_TERMS_DATA_H_
 #define CHROME_BROWSER_SEARCH_ENGINES_SEARCH_TERMS_DATA_H_
 #pragma once
 
 #include <string>
 
 #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 {
  public:
   SearchTermsData();
   virtual ~SearchTermsData();
 
   // Returns the value for the GOOGLE_BASE_SUGGEST_URL term.
   std::string GoogleBaseSuggestURLValue() const;
 
   // Returns the value to use for replacements of type GOOGLE_BASE_URL.
   virtual std::string GoogleBaseURLValue() const = 0;
 
   // Returns the locale used by the application.
   virtual std::string GetApplicationLocale() const = 0;
 
 #if defined(OS_WIN) && defined(GOOGLE_CHROME_BUILD)
   // Returns the value for the Chrome Omnibox rlz.
   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.
+  virtual std::string InstantFieldTrialUrlParam() const;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(SearchTermsData);
 };
 
 // Implementation of SearchTermsData that is only usable on the UI thread.
 class UIThreadSearchTermsData : public SearchTermsData {
  public:
-  UIThreadSearchTermsData();
+  // |profile| is needed only to create URL params related to the Instant field
+  // trial. Most users don't care about those params, so it's okay to pass in a
+  // NULL profile.
+  explicit UIThreadSearchTermsData(Profile* profile);

[Peter Kasting, 2011/08/11 00:35:17]

I wonder if it would be even simpler to leave this as a no-arg constructor and
instead have a set_profile() method.  Then only the (one?) spot that cares about
providing a profile to this struct would have to be touched.

 
   // Implementation of SearchTermsData.
   virtual std::string GoogleBaseURLValue() const;
   virtual std::string GetApplicationLocale() const;
 #if defined(OS_WIN) && defined(GOOGLE_CHROME_BUILD)
   virtual string16 GetRlzParameterValue() const;
 #endif
+  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* const profile_;
+
   DISALLOW_COPY_AND_ASSIGN(UIThreadSearchTermsData);
 };
 
 #endif  // CHROME_BROWSER_SEARCH_ENGINES_SEARCH_TERMS_DATA_H_