Create a ManagedModeNavigationObserver only for managed users.

chrome/browser/managed_mode/managed_mode_navigation_observer.cc

 // Copyright (c) 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/managed_mode/managed_mode_navigation_observer.h"
 
 #include "base/bind.h"
 #include "base/i18n/rtl.h"
 #include "base/metrics/histogram.h"
 #include "base/prefs/pref_service.h"
@@ skipping 381 matching lines @@
   DVLOG(1) << "NavigateToPendingEntry " << url.spec();
   // This method gets called only when the user goes back and forward and when
   // the user types a new URL. So do the main work in
   // ProvisionalChangeToMainFrameUrl and only check that the user didn't go
   // back to a blocked site here.
   ManagedModeURLFilter::FilteringBehavior behavior =
       url_filter_->GetFilteringBehaviorForURL(url);
   int current_index = web_contents()->GetController().GetCurrentEntryIndex();
   // First check that the user didn't go back to a blocked page, then check
   // that the navigation is allowed.
-  if (last_allowed_page_ < 0 || current_index <= last_allowed_page_ ||
+  if (current_index <= last_allowed_page_ ||
       (behavior == ManagedModeURLFilter::BLOCK &&
        !CanTemporarilyNavigateHost(url))) {
     ClearObserverState();
   }
   finished_redirects_ = false;
 }
 
 void ManagedModeNavigationObserver::DidNavigateMainFrame(
     const content::LoadCommittedDetails& details,
     const content::FrameNavigateParams& params) {
@@ skipping 105 matching lines @@
 
   if (behavior == ManagedModeURLFilter::BLOCK) {
     DCHECK_EQ(RECORDING_URLS_AFTER_PREVIEW, state_);
     // Add the infobar.
     if (!preview_infobar_delegate_) {
       preview_infobar_delegate_ = ManagedModePreviewInfobarDelegate::Create(
           InfoBarService::FromWebContents(web_contents()));
     }
   }
 }