Remove single active state restriction.

ios/web/active_state_manager_impl.mm

 // Copyright 2015 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 "ios/web/active_state_manager_impl.h"
 
 #include "base/logging.h"
 #include "ios/web/public/browser_state.h"
 #include "ios/web/public/web_thread.h"
 
 namespace web {
 
-namespace {
-// The number of ActiveStateManagers that are currently in active state.
-// At most one ActiveStateManager can be active at any given time.
-int g_active_state_manager_active_count = 0;
-}  // namespace
-
 ActiveStateManagerImpl::ActiveStateManagerImpl(BrowserState* browser_state)
     : browser_state_(browser_state), active_(false) {
   DCHECK_CURRENTLY_ON(WebThread::UI);
   DCHECK(browser_state_);
 }
 
 ActiveStateManagerImpl::~ActiveStateManagerImpl() {
   FOR_EACH_OBSERVER(Observer, observer_list_, WillBeDestroyed());
   DCHECK(!IsActive());
 }
 
 void ActiveStateManagerImpl::SetActive(bool active) {
   DCHECK_CURRENTLY_ON(WebThread::UI);
 
   if (active == active_) {
     return;
   }
-  if (active) {
-    ++g_active_state_manager_active_count;
-  } else {
-    --g_active_state_manager_active_count;
-  }
-  DCHECK_GE(1, g_active_state_manager_active_count);
   active_ = active;
 
   if (active) {
     FOR_EACH_OBSERVER(Observer, observer_list_, OnActive());
   } else {
     FOR_EACH_OBSERVER(Observer, observer_list_, OnInactive());
   }
 }
 
 bool ActiveStateManagerImpl::IsActive() {
   DCHECK_CURRENTLY_ON(WebThread::UI);
   return active_;
 }
 
 void ActiveStateManagerImpl::AddObserver(ActiveStateManager::Observer* obs) {
   DCHECK_CURRENTLY_ON(WebThread::UI);
   observer_list_.AddObserver(obs);
 }
 
 void ActiveStateManagerImpl::RemoveObserver(ActiveStateManager::Observer* obs) {
   DCHECK_CURRENTLY_ON(WebThread::UI);
   observer_list_.RemoveObserver(obs);
 }
 
 }  // namespace web