Instant: Use only one hidden WebContents per profile.

chrome/browser/instant/search.cc

Index: chrome/browser/instant/search.cc
diff --git a/chrome/browser/instant/search.cc b/chrome/browser/instant/search.cc
index 2816d5250fcd482487b0feb49968e12830d62cdf..6c1b3307aab6ce4c217c29cab3eec5a3ac369591 100644
--- a/chrome/browser/instant/search.cc
+++ b/chrome/browser/instant/search.cc
@@ -188,7 +188,7 @@ string16 GetSearchTermsImpl(const content::WebContents* contents,
   // faking search terms in the URL. Random pages can't get into the Instant
   // renderer and scripting doesn't work cross-process, so if the page is in
   // the Instant process, we know it isn't being exploited.
-  // Since iOS and Android doesn't use the instant framework, these checks are
+  // Since iOS and Android don't use the Instant framework, these checks are
   // disabled for the two platforms.
   Profile* profile = Profile::FromBrowserContext(contents->GetBrowserContext());
 #if !defined(OS_IOS) && !defined(OS_ANDROID)
@@ -323,6 +323,10 @@ 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() {