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..d8bc0ba78b116d02e158c45473501703b35695ad 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 +34,11 @@ 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.
+  virtual std::string InstantFieldTrialUrlParam() const;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(SearchTermsData);
 };
@@ -39,7 +46,10 @@ class 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;
@@ -47,6 +57,7 @@ class UIThreadSearchTermsData : public SearchTermsData {
 #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.
@@ -55,6 +66,8 @@ class UIThreadSearchTermsData : public SearchTermsData {
  private:
   static std::string* google_base_url_;
 
+  Profile* const profile_;
+
   DISALLOW_COPY_AND_ASSIGN(UIThreadSearchTermsData);
 };