Instant: Use only one hidden WebContents per profile.

chrome/browser/ui/search/search.cc

Index: chrome/browser/ui/search/search.cc
diff --git a/chrome/browser/ui/search/search.cc b/chrome/browser/ui/search/search.cc
index 6544bd1423f326f6311f8b8561ca1cc0404ec09f..5200fdd469b5b093388f86c91aa068f6977c3bfb 100644
--- a/chrome/browser/ui/search/search.cc
+++ b/chrome/browser/ui/search/search.cc
@@ -318,6 +318,10 @@ void RegisterUserPrefs(PrefRegistrySyncable* registry) {
   // This default is overridden by SetInstantExtendedPrefDefault().
   registry->RegisterBooleanPref(prefs::kInstantExtendedEnabled, false,
                                 PrefRegistrySyncable::SYNCABLE_PREF);
+
+  // TODO(jered): Remove this.
+  registry->RegisterStringPref(prefs::kInstantUIZeroSuggestUrlPrefix, "",
+                               PrefRegistrySyncable::UNSYNCABLE_PREF);
 }
 
 const char* GetInstantPrefName() {