Remove unused lock, add debug-only verification of intended usage.

chrome/browser/content_settings/host_content_settings_map.h

 // 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.
 
 // Maps hostnames to custom content settings.  Written on the UI thread and read
 // on any thread.  One instance per profile.
 
 #ifndef CHROME_BROWSER_CONTENT_SETTINGS_HOST_CONTENT_SETTINGS_MAP_H_
 #define CHROME_BROWSER_CONTENT_SETTINGS_HOST_CONTENT_SETTINGS_MAP_H_
 
 #include <map>
 #include <string>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/memory/ref_counted.h"
 #include "base/prefs/public/pref_change_registrar.h"
-#include "base/synchronization/lock.h"
 #include "base/tuple.h"
 #include "chrome/browser/content_settings/content_settings_observer.h"
 #include "chrome/common/content_settings.h"
 #include "chrome/common/content_settings_pattern.h"
 #include "chrome/common/content_settings_types.h"
 
 namespace base {
 class Value;
 }  // namespace base
 
@@ skipping 194 matching lines @@
   // from the normal mode. Otherwise, adds the content settings for the normal
   // mode.
   void AddSettingsForOneType(
       const content_settings::ProviderInterface* provider,
       ProviderType provider_type,
       ContentSettingsType content_type,
       const std::string& resource_identifier,
       ContentSettingsForOneType* settings,
       bool incognito) const;
 
+  // Call UsedContentSettingsProviders() whenever you access
+  // content_settings_providers_ (apart from initialization and
+  // teardown), so that we can DCHECK in RegisterExtensionService that
+  // it is not being called too late.
+  void UsedContentSettingsProviders() const;
+
+#ifndef NDEBUG
+  mutable bool used_content_settings_providers_;
+#endif
+
   // Weak; owned by the Profile.
   PrefService* prefs_;
 
   // Whether this settings map is for an OTR session.
   bool is_off_the_record_;
 
-  // Content setting providers.
+  // Content setting providers. This is only modified at construction
+  // time and by RegisterExtensionService, both of which should happen
+  // before any other uses of it.
   ProviderMap content_settings_providers_;
 
-  // Used around accesses to the following objects to guarantee thread safety.
-  mutable base::Lock lock_;
-
   DISALLOW_COPY_AND_ASSIGN(HostContentSettingsMap);
 };
 
 #endif  // CHROME_BROWSER_CONTENT_SETTINGS_HOST_CONTENT_SETTINGS_MAP_H_