Move instant support to SearchTabHelper. Fix InstantTab reset.

chrome/browser/ui/search/instant_tab.cc

 // Copyright 2012 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.
 
 #include "chrome/browser/ui/search/instant_tab.h"
 
 InstantTab::InstantTab(InstantPage::Delegate* delegate)
     : InstantPage(delegate, "") {
 }
 
 InstantTab::~InstantTab() {
 }
 
 void InstantTab::Init(content::WebContents* contents) {
   SetContents(contents);
-  DetermineIfPageSupportsInstant();
 }
 
 bool InstantTab::ShouldProcessSetSuggestions() {
   return true;
 }
 
 bool InstantTab::ShouldProcessFocusOmnibox() {
   return true;
 }
 
 bool InstantTab::ShouldProcessNavigateToURL() {
   return true;
 }