Introduce a field trial for Instant.

chrome/browser/autocomplete/autocomplete.h

Index: chrome/browser/autocomplete/autocomplete.h
diff --git a/chrome/browser/autocomplete/autocomplete.h b/chrome/browser/autocomplete/autocomplete.h
index 2a195451c6773884feb5b0d191ea21374bf93513..487e8bc3d373e34e9603c3821b66c24aa9a24851 100644
--- a/chrome/browser/autocomplete/autocomplete.h
+++ b/chrome/browser/autocomplete/autocomplete.h
@@ -599,13 +599,14 @@ class AutocompleteController : public ACProviderListener {
   AutocompleteController(Profile* profile,
                          AutocompleteControllerDelegate* delegate);
 #ifdef UNIT_TEST
-  explicit AutocompleteController(const ACProviders& providers)
+  AutocompleteController(const ACProviders& providers, Profile* profile)
       : delegate_(NULL),
         providers_(providers),
         keyword_provider_(NULL),
         search_provider_(NULL),
         done_(true),
-        in_start_(false) {
+        in_start_(false),
+        profile_(profile) {
   }
 #endif
   ~AutocompleteController();
@@ -728,6 +729,8 @@ class AutocompleteController : public ACProviderListener {
   // notifications until Start() has been invoked on all providers.
   bool in_start_;
 
+  Profile* profile_;
+
   DISALLOW_COPY_AND_ASSIGN(AutocompleteController);
 };