ObserverList::HasObserver now takes a const pointer.

Updated all clients that wrap HasObserver and expose it to also take a
const pointer. This change avoids further propagation of non-constness
(which was previously required when using HasObserver methods).

BUG=429588
TBR=michaeln@chromium.org,nyquist@chromium.org,pkotwicz@chromium.org,satorux@chromium.org,sky@chromium.org,zea@chromium.org

Review URL: https://codereview.chromium.org/697953002

Cr-Commit-Position: refs/heads/master@{#303428}

56 files changed, 81 insertions, 67 deletions

diff --git a/ash/wm/lock_state_controller.cc b/ash/wm/lock_state_controller.cc
index a03a958..7ba8a2f 100644
--- a/ash/wm/lock_state_controller.cc
+++ b/ash/wm/lock_state_controller.cc
@@ -85,7 +85,7 @@ void LockStateController::RemoveObserver(LockStateObserver* observer) {
   observers_.RemoveObserver(observer);
 }
 
-bool LockStateController::HasObserver(LockStateObserver* observer) {
+bool LockStateController::HasObserver(const LockStateObserver* observer) const {
   return observers_.HasObserver(observer);
 }
 
diff --git a/ash/wm/lock_state_controller.h b/ash/wm/lock_state_controller.h
index 73199bf..c039814 100644
--- a/ash/wm/lock_state_controller.h
+++ b/ash/wm/lock_state_controller.h
@@ -149,7 +149,7 @@ class ASH_EXPORT LockStateController : public aura::WindowTreeHostObserver,
 
   void AddObserver(LockStateObserver* observer);
   void RemoveObserver(LockStateObserver* observer);
-  bool HasObserver(LockStateObserver* observer);
+  bool HasObserver(const LockStateObserver* observer) const;
 
   // Starts locking (with slow animation) that can be cancelled.
   // After locking and |kLockToShutdownTimeoutMs| StartShutdownAnimation()
diff --git a/base/observer_list.h b/base/observer_list.h
index c77ec15..ef45269 100644
--- a/base/observer_list.h
+++ b/base/observer_list.h
@@ -100,7 +100,8 @@ class ObserverListBase
   // Remove an observer from the list if it is in the list.
   void RemoveObserver(ObserverType* obs);
 
-  bool HasObserver(ObserverType* observer) const;
+  // Determine whether a particular observer is in the list.
+  bool HasObserver(const ObserverType* observer) const;
 
   void Clear();
 
@@ -176,7 +177,8 @@ void ObserverListBase<ObserverType>::RemoveObserver(ObserverType* obs) {
 }
 
 template <class ObserverType>
-bool ObserverListBase<ObserverType>::HasObserver(ObserverType* observer) const {
+bool ObserverListBase<ObserverType>::HasObserver(
+    const ObserverType* observer) const {
   for (size_t i = 0; i < observers_.size(); ++i) {
     if (observers_[i] == observer)
       return true;
diff --git a/base/observer_list_unittest.cc b/base/observer_list_unittest.cc
index 11f59be..65ef934 100644
--- a/base/observer_list_unittest.cc
+++ b/base/observer_list_unittest.cc
@@ -182,6 +182,9 @@ TEST(ObserverListTest, BasicTest) {
   observer_list.AddObserver(&a);
   observer_list.AddObserver(&b);
 
+  EXPECT_TRUE(observer_list.HasObserver(&a));
+  EXPECT_FALSE(observer_list.HasObserver(&c));
+
   FOR_EACH_OBSERVER(Foo, observer_list, Observe(10));
 
   observer_list.AddObserver(&evil);
diff --git a/chrome/browser/chromeos/settings/device_settings_test_helper.cc b/chrome/browser/chromeos/settings/device_settings_test_helper.cc
index fed7034..fa16d49 100644
--- a/chrome/browser/chromeos/settings/device_settings_test_helper.cc
+++ b/chrome/browser/chromeos/settings/device_settings_test_helper.cc
@@ -100,7 +100,7 @@ void DeviceSettingsTestHelper::AddObserver(Observer* observer) {}
 
 void DeviceSettingsTestHelper::RemoveObserver(Observer* observer) {}
 
-bool DeviceSettingsTestHelper::HasObserver(Observer* observer) {
+bool DeviceSettingsTestHelper::HasObserver(const Observer* observer) const {
   return false;
 }
 
diff --git a/chrome/browser/chromeos/settings/device_settings_test_helper.h b/chrome/browser/chromeos/settings/device_settings_test_helper.h
index 8100563..54dcf9b 100644
--- a/chrome/browser/chromeos/settings/device_settings_test_helper.h
+++ b/chrome/browser/chromeos/settings/device_settings_test_helper.h
@@ -87,7 +87,7 @@ class DeviceSettingsTestHelper : public SessionManagerClient {
       override;
   virtual void AddObserver(Observer* observer) override;
   virtual void RemoveObserver(Observer* observer) override;
-  virtual bool HasObserver(Observer* observer) override;
+  virtual bool HasObserver(const Observer* observer) const override;
   virtual void EmitLoginPromptVisible() override;
   virtual void RestartJob(int pid, const std::string& command_line) override;
   virtual void StartSession(const std::string& user_email) override;
diff --git a/chrome/browser/extensions/api/dial/dial_registry_unittest.cc b/chrome/browser/extensions/api/dial/dial_registry_unittest.cc
index 6d5a0b4..69dd839 100644
--- a/chrome/browser/extensions/api/dial/dial_registry_unittest.cc
+++ b/chrome/browser/extensions/api/dial/dial_registry_unittest.cc
@@ -35,7 +35,7 @@ class MockDialService : public DialService {
   MOCK_METHOD0(Discover, bool());
   MOCK_METHOD1(AddObserver, void(DialService::Observer*));
   MOCK_METHOD1(RemoveObserver, void(DialService::Observer*));
-  MOCK_METHOD1(HasObserver, bool(DialService::Observer*));
+  MOCK_CONST_METHOD1(HasObserver, bool(const DialService::Observer*));
 };
 
 class MockDialRegistry : public DialRegistry {
diff --git a/chrome/browser/extensions/api/dial/dial_service.cc b/chrome/browser/extensions/api/dial/dial_service.cc
index 18311df..4197d62 100644
--- a/chrome/browser/extensions/api/dial/dial_service.cc
+++ b/chrome/browser/extensions/api/dial/dial_service.cc
@@ -407,7 +407,7 @@ void DialServiceImpl::RemoveObserver(Observer* observer) {
   observer_list_.RemoveObserver(observer);
 }
 
-bool DialServiceImpl::HasObserver(Observer* observer) {
+bool DialServiceImpl::HasObserver(const Observer* observer) const {
   DCHECK(thread_checker_.CalledOnValidThread());
   return observer_list_.HasObserver(observer);
 }
diff --git a/chrome/browser/extensions/api/dial/dial_service.h b/chrome/browser/extensions/api/dial/dial_service.h
index b70ca46..6816624 100644
--- a/chrome/browser/extensions/api/dial/dial_service.h
+++ b/chrome/browser/extensions/api/dial/dial_service.h
@@ -89,7 +89,7 @@ class DialService {
   // Called by listeners to this service to add/remove themselves as observers.
   virtual void AddObserver(Observer* observer) = 0;
   virtual void RemoveObserver(Observer* observer) = 0;
-  virtual bool HasObserver(Observer* observer) = 0;
+  virtual bool HasObserver(const Observer* observer) const = 0;
 };
 
 // Implements DialService.
@@ -108,7 +108,7 @@ class DialServiceImpl : public DialService,
   bool Discover() override;
   void AddObserver(Observer* observer) override;
   void RemoveObserver(Observer* observer) override;
-  bool HasObserver(Observer* observer) override;
+  bool HasObserver(const Observer* observer) const override;
 
  private:
   // Represents a socket binding to a single network interface.
diff --git a/chrome/browser/search/instant_unittest_base.cc b/chrome/browser/search/instant_unittest_base.cc
index 23aa5ed..38aedb4 100644
--- a/chrome/browser/search/instant_unittest_base.cc
+++ b/chrome/browser/search/instant_unittest_base.cc
@@ -78,7 +78,7 @@ void InstantUnitTestBase::NotifyGoogleBaseURLUpdate(
 }
 
 bool InstantUnitTestBase::IsInstantServiceObserver(
-    InstantServiceObserver* observer) {
+    const InstantServiceObserver* observer) const {
   return instant_service_->observers_.HasObserver(observer);
 }
 
diff --git a/chrome/browser/search/instant_unittest_base.h b/chrome/browser/search/instant_unittest_base.h
index a99b2f0..267895a 100644
--- a/chrome/browser/search/instant_unittest_base.h
+++ b/chrome/browser/search/instant_unittest_base.h
@@ -42,7 +42,7 @@ class InstantUnitTestBase : public BrowserWithTestWindowTest {
   // tests, so this is required.
   void NotifyGoogleBaseURLUpdate(const std::string& new_google_base_url);
 
-  bool IsInstantServiceObserver(InstantServiceObserver* observer);
+  bool IsInstantServiceObserver(const InstantServiceObserver* observer) const;
 
   InstantService* instant_service_;
   TemplateURLService* template_url_service_;
diff --git a/chrome/browser/sync/backend_migrator.cc b/chrome/browser/sync/backend_migrator.cc
index 45668cb..87ddc5b 100644
--- a/chrome/browser/sync/backend_migrator.cc
+++ b/chrome/browser/sync/backend_migrator.cc
@@ -75,7 +75,7 @@ void BackendMigrator::AddMigrationObserver(MigrationObserver* observer) {
 }
 
 bool BackendMigrator::HasMigrationObserver(
-    MigrationObserver* observer) const {
+    const MigrationObserver* observer) const {
   return migration_observers_.HasObserver(observer);
 }
 
diff --git a/chrome/browser/sync/backend_migrator.h b/chrome/browser/sync/backend_migrator.h
index c34520d..64bce1a 100644
--- a/chrome/browser/sync/backend_migrator.h
+++ b/chrome/browser/sync/backend_migrator.h
@@ -58,7 +58,7 @@ class BackendMigrator {
   void MigrateTypes(syncer::ModelTypeSet types);
 
   void AddMigrationObserver(MigrationObserver* observer);
-  bool HasMigrationObserver(MigrationObserver* observer) const;
+  bool HasMigrationObserver(const MigrationObserver* observer) const;
   void RemoveMigrationObserver(MigrationObserver* observer);
 
   State state() const;
diff --git a/chrome/browser/sync/profile_sync_service.cc b/chrome/browser/sync/profile_sync_service.cc
index 9fb4b92..3eefdde 100644
--- a/chrome/browser/sync/profile_sync_service.cc
+++ b/chrome/browser/sync/profile_sync_service.cc
@@ -2439,7 +2439,7 @@ void ProfileSyncService::GetAllNodes(
 }
 
 bool ProfileSyncService::HasObserver(
-    ProfileSyncServiceBase::Observer* observer) const {
+    const ProfileSyncServiceBase::Observer* observer) const {
   return observers_.HasObserver(observer);
 }
 
diff --git a/chrome/browser/sync/profile_sync_service.h b/chrome/browser/sync/profile_sync_service.h
index a8bcc3c..b70b9dc 100644
--- a/chrome/browser/sync/profile_sync_service.h
+++ b/chrome/browser/sync/profile_sync_service.h
@@ -289,7 +289,8 @@ class ProfileSyncService : public ProfileSyncServiceBase,
   syncer::ModelTypeSet GetActiveDataTypes() const override;
   void AddObserver(ProfileSyncServiceBase::Observer* observer) override;
   void RemoveObserver(ProfileSyncServiceBase::Observer* observer) override;
-  bool HasObserver(ProfileSyncServiceBase::Observer* observer) const override;
+  bool HasObserver(
+      const ProfileSyncServiceBase::Observer* observer) const override;
 
   void AddProtocolEventObserver(browser_sync::ProtocolEventObserver* observer);
   void RemoveProtocolEventObserver(
diff --git a/chrome/browser/sync/profile_sync_service_base.h b/chrome/browser/sync/profile_sync_service_base.h
index 57f1ba6..8f0b8f3 100644
--- a/chrome/browser/sync/profile_sync_service_base.h
+++ b/chrome/browser/sync/profile_sync_service_base.h
@@ -51,7 +51,7 @@ class ProfileSyncServiceBase {
   virtual void RemoveObserver(Observer* observer) = 0;
 
   // Returns true if |observer| has already been added as an observer.
-  virtual bool HasObserver(Observer* observer) const = 0;
+  virtual bool HasObserver(const Observer* observer) const = 0;
 };
 
 #endif  // CHROME_BROWSER_SYNC_PROFILE_SYNC_SERVICE_BASE_H_
diff --git a/chrome/browser/ui/ash/screenshot_taker.cc b/chrome/browser/ui/ash/screenshot_taker.cc
index 6cac097..108ca8b 100644
--- a/chrome/browser/ui/ash/screenshot_taker.cc
+++ b/chrome/browser/ui/ash/screenshot_taker.cc
@@ -535,7 +535,8 @@ void ScreenshotTaker::RemoveObserver(ScreenshotTakerObserver* observer) {
   observers_.RemoveObserver(observer);
 }
 
-bool ScreenshotTaker::HasObserver(ScreenshotTakerObserver* observer) const {
+bool ScreenshotTaker::HasObserver(
+    const ScreenshotTakerObserver* observer) const {
   return observers_.HasObserver(observer);
 }
 
diff --git a/chrome/browser/ui/ash/screenshot_taker.h b/chrome/browser/ui/ash/screenshot_taker.h
index fd46bbe..3903956 100644
--- a/chrome/browser/ui/ash/screenshot_taker.h
+++ b/chrome/browser/ui/ash/screenshot_taker.h
@@ -67,7 +67,7 @@ class ScreenshotTaker : public ash::ScreenshotDelegate {
 
   void AddObserver(ScreenshotTakerObserver* observer);
   void RemoveObserver(ScreenshotTakerObserver* observer);
-  bool HasObserver(ScreenshotTakerObserver* observer) const;
+  bool HasObserver(const ScreenshotTakerObserver* observer) const;
 
  private:
   friend class ash::test::ScreenshotTakerTest;
diff --git a/chromeos/dbus/cras_audio_client.cc b/chromeos/dbus/cras_audio_client.cc
index b756ee6..189a272 100644
--- a/chromeos/dbus/cras_audio_client.cc
+++ b/chromeos/dbus/cras_audio_client.cc
@@ -36,7 +36,7 @@ class CrasAudioClientImpl : public CrasAudioClient {
     observers_.RemoveObserver(observer);
   }
 
-  virtual bool HasObserver(Observer* observer) override {
+  virtual bool HasObserver(const Observer* observer) const override {
     return observers_.HasObserver(observer);
   }
 
diff --git a/chromeos/dbus/cras_audio_client.h b/chromeos/dbus/cras_audio_client.h
index 737d266..be93eaf 100644
--- a/chromeos/dbus/cras_audio_client.h
+++ b/chromeos/dbus/cras_audio_client.h
@@ -49,7 +49,7 @@ class CHROMEOS_EXPORT CrasAudioClient : public DBusClient {
   virtual void AddObserver(Observer* observer) = 0;
   virtual void RemoveObserver(Observer* observer) = 0;
   // Returns true if this object has the given observer.
-  virtual bool HasObserver(Observer* observer) = 0;
+  virtual bool HasObserver(const Observer* observer) const = 0;
 
   // GetVolumeStateCallback is used for GetVolumeState method. It receives
   // 2 arguments, |volume_state| which containing both input and  output volume
diff --git a/chromeos/dbus/fake_cras_audio_client.cc b/chromeos/dbus/fake_cras_audio_client.cc
index 6c8f941..b2135aa 100644
--- a/chromeos/dbus/fake_cras_audio_client.cc
+++ b/chromeos/dbus/fake_cras_audio_client.cc
@@ -68,7 +68,7 @@ void FakeCrasAudioClient::RemoveObserver(Observer* observer) {
   observers_.RemoveObserver(observer);
 }
 
-bool FakeCrasAudioClient::HasObserver(Observer* observer) {
+bool FakeCrasAudioClient::HasObserver(const Observer* observer) const {
   return observers_.HasObserver(observer);
 }
 
diff --git a/chromeos/dbus/fake_cras_audio_client.h b/chromeos/dbus/fake_cras_audio_client.h
index 07fd908..c68e3a3 100644
--- a/chromeos/dbus/fake_cras_audio_client.h
+++ b/chromeos/dbus/fake_cras_audio_client.h
@@ -22,7 +22,7 @@ class CHROMEOS_EXPORT FakeCrasAudioClient : public CrasAudioClient {
   virtual void Init(dbus::Bus* bus) override;
   virtual void AddObserver(Observer* observer) override;
   virtual void RemoveObserver(Observer* observer) override;
-  virtual bool HasObserver(Observer* observer) override;
+  virtual bool HasObserver(const Observer* observer) const override;
   virtual void GetVolumeState(const GetVolumeStateCallback& callback) override;
   virtual void GetNodes(const GetNodesCallback& callback,
                         const ErrorCallback& error_callback) override;
diff --git a/chromeos/dbus/fake_power_manager_client.cc b/chromeos/dbus/fake_power_manager_client.cc
index 7136dfb..bfb5f71 100644
--- a/chromeos/dbus/fake_power_manager_client.cc
+++ b/chromeos/dbus/fake_power_manager_client.cc
@@ -34,7 +34,7 @@ void FakePowerManagerClient::RemoveObserver(Observer* observer) {
   observers_.RemoveObserver(observer);
 }
 
-bool FakePowerManagerClient::HasObserver(Observer* observer) {
+bool FakePowerManagerClient::HasObserver(const Observer* observer) const {
   return false;
 }
 
diff --git a/chromeos/dbus/fake_power_manager_client.h b/chromeos/dbus/fake_power_manager_client.h
index c81ec85..d840d51 100644
--- a/chromeos/dbus/fake_power_manager_client.h
+++ b/chromeos/dbus/fake_power_manager_client.h
@@ -37,7 +37,7 @@ class FakePowerManagerClient : public PowerManagerClient {
   virtual void Init(dbus::Bus* bus) override;
   virtual void AddObserver(Observer* observer) override;
   virtual void RemoveObserver(Observer* observer) override;
-  virtual bool HasObserver(Observer* observer) override;
+  virtual bool HasObserver(const Observer* observer) const override;
   virtual void DecreaseScreenBrightness(bool allow_off) override;
   virtual void IncreaseScreenBrightness() override;
   virtual void SetScreenBrightnessPercent(
diff --git a/chromeos/dbus/fake_session_manager_client.cc b/chromeos/dbus/fake_session_manager_client.cc
index c5fe549..fab7c3c 100644
--- a/chromeos/dbus/fake_session_manager_client.cc
+++ b/chromeos/dbus/fake_session_manager_client.cc
@@ -35,7 +35,7 @@ void FakeSessionManagerClient::RemoveObserver(Observer* observer) {
   observers_.RemoveObserver(observer);
 }
 
-bool FakeSessionManagerClient::HasObserver(Observer* observer) {
+bool FakeSessionManagerClient::HasObserver(const Observer* observer) const {
   return observers_.HasObserver(observer);
 }
 
diff --git a/chromeos/dbus/fake_session_manager_client.h b/chromeos/dbus/fake_session_manager_client.h
index f69e262..8630e86 100644
--- a/chromeos/dbus/fake_session_manager_client.h
+++ b/chromeos/dbus/fake_session_manager_client.h
@@ -28,7 +28,7 @@ class FakeSessionManagerClient : public SessionManagerClient {
   virtual void SetStubDelegate(StubDelegate* delegate) override;
   virtual void AddObserver(Observer* observer) override;
   virtual void RemoveObserver(Observer* observer) override;
-  virtual bool HasObserver(Observer* observer) override;
+  virtual bool HasObserver(const Observer* observer) const override;
   virtual void EmitLoginPromptVisible() override;
   virtual void RestartJob(int pid, const std::string& command_line) override;
   virtual void StartSession(const std::string& user_email) override;
diff --git a/chromeos/dbus/fake_system_clock_client.cc b/chromeos/dbus/fake_system_clock_client.cc
index c744bdd..b2ee3c6 100644
--- a/chromeos/dbus/fake_system_clock_client.cc
+++ b/chromeos/dbus/fake_system_clock_client.cc
@@ -21,7 +21,7 @@ void FakeSystemClockClient::AddObserver(Observer* observer) {
 void FakeSystemClockClient::RemoveObserver(Observer* observer) {
 }
 
-bool FakeSystemClockClient::HasObserver(Observer* observer) {
+bool FakeSystemClockClient::HasObserver(const Observer* observer) const {
   return false;
 }
 
diff --git a/chromeos/dbus/fake_system_clock_client.h b/chromeos/dbus/fake_system_clock_client.h
index a53ff87..104f514 100644
--- a/chromeos/dbus/fake_system_clock_client.h
+++ b/chromeos/dbus/fake_system_clock_client.h
@@ -19,7 +19,7 @@ class CHROMEOS_EXPORT FakeSystemClockClient : public SystemClockClient {
   virtual void Init(dbus::Bus* bus) override;
   virtual void AddObserver(Observer* observer) override;
   virtual void RemoveObserver(Observer* observer) override;
-  virtual bool HasObserver(Observer* observer) override;
+  virtual bool HasObserver(const Observer* observer) const override;
   virtual void SetTime(int64 time_in_seconds) override;
   virtual bool CanSetTime() override;
 
diff --git a/chromeos/dbus/fake_update_engine_client.cc b/chromeos/dbus/fake_update_engine_client.cc
index 53314e2..a594a3e 100644
--- a/chromeos/dbus/fake_update_engine_client.cc
+++ b/chromeos/dbus/fake_update_engine_client.cc
@@ -29,7 +29,7 @@ void FakeUpdateEngineClient::RemoveObserver(Observer* observer) {
   observers_.RemoveObserver(observer);
 }
 
-bool FakeUpdateEngineClient::HasObserver(Observer* observer) {
+bool FakeUpdateEngineClient::HasObserver(const Observer* observer) const {
   return observers_.HasObserver(observer);
 }
 
diff --git a/chromeos/dbus/fake_update_engine_client.h b/chromeos/dbus/fake_update_engine_client.h
index 6475f2c..db61d0e 100644
--- a/chromeos/dbus/fake_update_engine_client.h
+++ b/chromeos/dbus/fake_update_engine_client.h
@@ -25,7 +25,7 @@ class FakeUpdateEngineClient : public UpdateEngineClient {
   virtual void Init(dbus::Bus* bus) override;
   virtual void AddObserver(Observer* observer) override;
   virtual void RemoveObserver(Observer* observer) override;
-  virtual bool HasObserver(Observer* observer) override;
+  virtual bool HasObserver(const Observer* observer) const override;
   virtual void RequestUpdateCheck(const UpdateCheckCallback& callback) override;
   virtual void RebootAfterUpdate() override;
   virtual void Rollback() override;
diff --git a/chromeos/dbus/mock_session_manager_client.h b/chromeos/dbus/mock_session_manager_client.h
index c0e4531..78972ce7 100644
--- a/chromeos/dbus/mock_session_manager_client.h
+++ b/chromeos/dbus/mock_session_manager_client.h
@@ -21,7 +21,7 @@ class MockSessionManagerClient : public SessionManagerClient {
   MOCK_METHOD1(SetStubDelegate, void(StubDelegate* delegate));
   MOCK_METHOD1(AddObserver, void(Observer*));
   MOCK_METHOD1(RemoveObserver, void(Observer*));
-  MOCK_METHOD1(HasObserver, bool(Observer*));
+  MOCK_CONST_METHOD1(HasObserver, bool(const Observer*));
   MOCK_METHOD0(EmitLoginPromptVisible, void(void));
   MOCK_METHOD2(RestartJob, void(int, const std::string&));
   MOCK_METHOD1(StartSession, void(const std::string&));
diff --git a/chromeos/dbus/power_manager_client.cc b/chromeos/dbus/power_manager_client.cc
index b2e8416..4192e0d 100644
--- a/chromeos/dbus/power_manager_client.cc
+++ b/chromeos/dbus/power_manager_client.cc
@@ -78,7 +78,7 @@ class PowerManagerClientImpl : public PowerManagerClient {
     observers_.RemoveObserver(observer);
   }
 
-  virtual bool HasObserver(Observer* observer) override {
+  virtual bool HasObserver(const Observer* observer) const override {
     return observers_.HasObserver(observer);
   }
 
@@ -780,7 +780,7 @@ class PowerManagerClientStubImpl : public PowerManagerClient {
     observers_.RemoveObserver(observer);
   }
 
-  virtual bool HasObserver(Observer* observer) override {
+  virtual bool HasObserver(const Observer* observer) const override {
     return observers_.HasObserver(observer);
   }
 
diff --git a/chromeos/dbus/power_manager_client.h b/chromeos/dbus/power_manager_client.h
index be598d5..b688002 100644
--- a/chromeos/dbus/power_manager_client.h
+++ b/chromeos/dbus/power_manager_client.h
@@ -100,7 +100,7 @@ class CHROMEOS_EXPORT PowerManagerClient : public DBusClient {
   // Adds and removes the observer.
   virtual void AddObserver(Observer* observer) = 0;
   virtual void RemoveObserver(Observer* observer) = 0;
-  virtual bool HasObserver(Observer* observer) = 0;
+  virtual bool HasObserver(const Observer* observer) const = 0;
 
   // Decreases the screen brightness. |allow_off| controls whether or not
   // it's allowed to turn off the back light.
diff --git a/chromeos/dbus/session_manager_client.cc b/chromeos/dbus/session_manager_client.cc
index 5a67ee8..a3e0ced 100644
--- a/chromeos/dbus/session_manager_client.cc
+++ b/chromeos/dbus/session_manager_client.cc
@@ -84,7 +84,7 @@ class SessionManagerClientImpl : public SessionManagerClient {
     observers_.RemoveObserver(observer);
   }
 
-  virtual bool HasObserver(Observer* observer) override {
+  virtual bool HasObserver(const Observer* observer) const override {
     return observers_.HasObserver(observer);
   }
 
@@ -583,7 +583,7 @@ class SessionManagerClientStubImpl : public SessionManagerClient {
   virtual void RemoveObserver(Observer* observer) override {
     observers_.RemoveObserver(observer);
   }
-  virtual bool HasObserver(Observer* observer) override {
+  virtual bool HasObserver(const Observer* observer) const override {
     return observers_.HasObserver(observer);
   }
   virtual void EmitLoginPromptVisible() override {}
diff --git a/chromeos/dbus/session_manager_client.h b/chromeos/dbus/session_manager_client.h
index d4c0706..346b131 100644
--- a/chromeos/dbus/session_manager_client.h
+++ b/chromeos/dbus/session_manager_client.h
@@ -63,7 +63,7 @@ class CHROMEOS_EXPORT SessionManagerClient : public DBusClient {
   // Adds and removes the observer.
   virtual void AddObserver(Observer* observer) = 0;
   virtual void RemoveObserver(Observer* observer) = 0;
-  virtual bool HasObserver(Observer* observer) = 0;
+  virtual bool HasObserver(const Observer* observer) const = 0;
 
   // Kicks off an attempt to emit the "login-prompt-visible" upstart signal.
   virtual void EmitLoginPromptVisible() = 0;
diff --git a/chromeos/dbus/system_clock_client.cc b/chromeos/dbus/system_clock_client.cc
index 65afc8a..9614c59 100644
--- a/chromeos/dbus/system_clock_client.cc
+++ b/chromeos/dbus/system_clock_client.cc
@@ -35,7 +35,7 @@ class SystemClockClientImpl : public SystemClockClient {
     observers_.RemoveObserver(observer);
   }
 
-  virtual bool HasObserver(Observer* observer) override {
+  virtual bool HasObserver(const Observer* observer) const override {
     return observers_.HasObserver(observer);
   }
 
diff --git a/chromeos/dbus/system_clock_client.h b/chromeos/dbus/system_clock_client.h
index 1757853..8380ff1 100644
--- a/chromeos/dbus/system_clock_client.h
+++ b/chromeos/dbus/system_clock_client.h
@@ -35,7 +35,7 @@ class CHROMEOS_EXPORT SystemClockClient : public DBusClient {
   // Removes the given observer if this object has the observer.
   virtual void RemoveObserver(Observer* observer) = 0;
   // Returns true if this object has the given observer.
-  virtual bool HasObserver(Observer* observer) = 0;
+  virtual bool HasObserver(const Observer* observer) const = 0;
 
   // Sets the system clock.
   virtual void SetTime(int64 time_in_seconds) = 0;
diff --git a/chromeos/dbus/update_engine_client.cc b/chromeos/dbus/update_engine_client.cc
index 6a777b5..19f3e06 100644
--- a/chromeos/dbus/update_engine_client.cc
+++ b/chromeos/dbus/update_engine_client.cc
@@ -98,7 +98,7 @@ class UpdateEngineClientImpl : public UpdateEngineClient {
     observers_.RemoveObserver(observer);
   }
 
-  virtual bool HasObserver(Observer* observer) override {
+  virtual bool HasObserver(const Observer* observer) const override {
     return observers_.HasObserver(observer);
   }
 
@@ -412,7 +412,9 @@ class UpdateEngineClientStubImpl : public UpdateEngineClient {
   virtual void Init(dbus::Bus* bus) override {}
   virtual void AddObserver(Observer* observer) override {}
   virtual void RemoveObserver(Observer* observer) override {}
-  virtual bool HasObserver(Observer* observer) override { return false; }
+  virtual bool HasObserver(const Observer* observer) const override {
+    return false;
+  }
 
   virtual void RequestUpdateCheck(
       const UpdateCheckCallback& callback) override {
@@ -467,7 +469,7 @@ class UpdateEngineClientFakeImpl : public UpdateEngineClientStubImpl {
       observers_.RemoveObserver(observer);
   }
 
-  virtual bool HasObserver(Observer* observer) override {
+  virtual bool HasObserver(const Observer* observer) const override {
     return observers_.HasObserver(observer);
   }
 
diff --git a/chromeos/dbus/update_engine_client.h b/chromeos/dbus/update_engine_client.h
index def8cb5..c92ddca 100644
--- a/chromeos/dbus/update_engine_client.h
+++ b/chromeos/dbus/update_engine_client.h
@@ -75,7 +75,7 @@ class CHROMEOS_EXPORT UpdateEngineClient : public DBusClient {
   virtual void AddObserver(Observer* observer) = 0;
   virtual void RemoveObserver(Observer* observer) = 0;
   // Returns true if this object has the given observer.
-  virtual bool HasObserver(Observer* observer) = 0;
+  virtual bool HasObserver(const Observer* observer) const = 0;
 
   // Called once RequestUpdateCheck() is complete. Takes one parameter:
   // - UpdateCheckResult: the result of the update check.
diff --git a/components/invalidation/invalidation_logger.cc b/components/invalidation/invalidation_logger.cc
index c0e8b41..c432686 100644
--- a/components/invalidation/invalidation_logger.cc
+++ b/components/invalidation/invalidation_logger.cc
@@ -116,7 +116,7 @@ void InvalidationLogger::UnregisterObserver(
 }
 
 bool InvalidationLogger::IsObserverRegistered(
-    InvalidationLoggerObserver* debug_observer) {
+    const InvalidationLoggerObserver* debug_observer) const {
   return observer_list_.HasObserver(debug_observer);
 }
 }  // namespace invalidation
diff --git a/components/invalidation/invalidation_logger.h b/components/invalidation/invalidation_logger.h
index 39d754e..e19ff07 100644
--- a/components/invalidation/invalidation_logger.h
+++ b/components/invalidation/invalidation_logger.h
@@ -60,7 +60,8 @@ class InvalidationLogger {
   // Add and remove observers listening for messages.
   void RegisterObserver(InvalidationLoggerObserver* debug_observer);
   void UnregisterObserver(InvalidationLoggerObserver* debug_observer);
-  bool IsObserverRegistered(InvalidationLoggerObserver* debug_observer);
+  bool IsObserverRegistered(
+      const InvalidationLoggerObserver* debug_observer) const;
 
  private:
   // Send to every Observer a OnStateChange event with the latest state.
diff --git a/components/invalidation/invalidator_registrar.cc b/components/invalidation/invalidator_registrar.cc
index 80cb7f6..9ee6a94 100644
--- a/components/invalidation/invalidator_registrar.cc
+++ b/components/invalidation/invalidator_registrar.cc
@@ -135,7 +135,7 @@ InvalidatorRegistrar::GetSanitizedHandlersIdsMap() {
 }
 
 bool InvalidatorRegistrar::IsHandlerRegisteredForTest(
-    InvalidationHandler* handler) const {
+    const InvalidationHandler* handler) const {
   DCHECK(thread_checker_.CalledOnValidThread());
   return handlers_.HasObserver(handler);
 }
diff --git a/components/invalidation/invalidator_registrar.h b/components/invalidation/invalidator_registrar.h
index f2e41a2..e6804bb 100644
--- a/components/invalidation/invalidator_registrar.h
+++ b/components/invalidation/invalidator_registrar.h
@@ -76,7 +76,7 @@ class INVALIDATION_EXPORT InvalidatorRegistrar {
   // to display every registered handlers and its objectsIds.
   std::map<std::string, ObjectIdSet> GetSanitizedHandlersIdsMap();
 
-  bool IsHandlerRegisteredForTest(InvalidationHandler* handler) const;
+  bool IsHandlerRegisteredForTest(const InvalidationHandler* handler) const;
 
   // Needed for death tests.
   void DetachFromThreadForTest();
diff --git a/content/browser/appcache/appcache_group.cc b/content/browser/appcache/appcache_group.cc
index 7ebd289..ce6d873 100644
--- a/content/browser/appcache/appcache_group.cc
+++ b/content/browser/appcache/appcache_group.cc
@@ -219,7 +219,9 @@ void AppCacheGroup::RunQueuedUpdates() {
   }
 }
 
-bool AppCacheGroup::FindObserver(UpdateObserver* find_me,
+// static
+bool AppCacheGroup::FindObserver(
+    const UpdateObserver* find_me,
     const ObserverList<UpdateObserver>& observer_list) {
   return observer_list.HasObserver(find_me);
 }
diff --git a/content/browser/appcache/appcache_group.h b/content/browser/appcache/appcache_group.h
index 3c54cfe..1a2df75 100644
--- a/content/browser/appcache/appcache_group.h
+++ b/content/browser/appcache/appcache_group.h
@@ -122,8 +122,8 @@ class CONTENT_EXPORT AppCacheGroup
   // Update cannot be processed at this time. Queue it for a later run.
   void QueueUpdate(AppCacheHost* host, const GURL& new_master_resource);
   void RunQueuedUpdates();
-  bool FindObserver(UpdateObserver* find_me,
-                    const ObserverList<UpdateObserver>& observer_list);
+  static bool FindObserver(const UpdateObserver* find_me,
+                           const ObserverList<UpdateObserver>& observer_list);
   void ScheduleUpdateRestart(int delay_ms);
   void HostDestructionImminent(AppCacheHost* host);
 
diff --git a/sync/sessions/model_type_registry.cc b/sync/sessions/model_type_registry.cc
index fdc0e40..2366f20 100644
--- a/sync/sessions/model_type_registry.cc
+++ b/sync/sessions/model_type_registry.cc
@@ -283,7 +283,7 @@ void ModelTypeRegistry::UnregisterDirectoryTypeDebugInfoObserver(
 }
 
 bool ModelTypeRegistry::HasDirectoryTypeDebugInfoObserver(
-    syncer::TypeDebugInfoObserver* observer) {
+    const syncer::TypeDebugInfoObserver* observer) const {
   return type_debug_info_observers_.HasObserver(observer);
 }
 
diff --git a/sync/sessions/model_type_registry.h b/sync/sessions/model_type_registry.h
index 22efdf5..bdd36d9 100644
--- a/sync/sessions/model_type_registry.h
+++ b/sync/sessions/model_type_registry.h
@@ -97,7 +97,7 @@ class SYNC_EXPORT_PRIVATE ModelTypeRegistry
   void UnregisterDirectoryTypeDebugInfoObserver(
       syncer::TypeDebugInfoObserver* observer);
   bool HasDirectoryTypeDebugInfoObserver(
-      syncer::TypeDebugInfoObserver* observer);
+      const syncer::TypeDebugInfoObserver* observer) const;
   void RequestEmitDebugInfo();
 
   base::WeakPtr<SyncContext> AsWeakPtr();
diff --git a/ui/app_list/app_list_model_unittest.cc b/ui/app_list/app_list_model_unittest.cc
index 93f0565..3e9eb02 100644
--- a/ui/app_list/app_list_model_unittest.cc
+++ b/ui/app_list/app_list_model_unittest.cc
@@ -75,8 +75,8 @@ class AppListModelTest : public testing::Test {
   void TearDown() override { model_.RemoveObserver(&observer_); }
 
  protected:
-  bool ItemObservedByFolder(AppListFolderItem* folder,
-                            AppListItem* item) {
+  static bool ItemObservedByFolder(AppListFolderItem* folder,
+                                   const AppListItem* item) {
     return item->observers_.HasObserver(folder->folder_image());
   }
 
diff --git a/ui/aura/window.cc b/ui/aura/window.cc
index 4d9cec7..c88826e 100644
--- a/ui/aura/window.cc
+++ b/ui/aura/window.cc
@@ -663,7 +663,7 @@ void Window::RemoveObserver(WindowObserver* observer) {
   observers_.RemoveObserver(observer);
 }
 
-bool Window::HasObserver(WindowObserver* observer) {
+bool Window::HasObserver(const WindowObserver* observer) const {
   return observers_.HasObserver(observer);
 }
 
diff --git a/ui/aura/window.h b/ui/aura/window.h
index 4f597eb..d1cff7b 100644
--- a/ui/aura/window.h
+++ b/ui/aura/window.h
@@ -223,7 +223,7 @@ class AURA_EXPORT Window : public ui::LayerDelegate,
   // Add/remove observer.
   void AddObserver(WindowObserver* observer);
   void RemoveObserver(WindowObserver* observer);
-  bool HasObserver(WindowObserver* observer);
+  bool HasObserver(const WindowObserver* observer) const;
 
   void set_ignore_events(bool ignore_events) { ignore_events_ = ignore_events; }
   bool ignore_events() const { return ignore_events_; }
diff --git a/ui/compositor/compositor.cc b/ui/compositor/compositor.cc
index cc44cec..35443f4 100644
--- a/ui/compositor/compositor.cc
+++ b/ui/compositor/compositor.cc
@@ -312,7 +312,7 @@ void Compositor::RemoveObserver(CompositorObserver* observer) {
   observer_list_.RemoveObserver(observer);
 }
 
-bool Compositor::HasObserver(CompositorObserver* observer) {
+bool Compositor::HasObserver(const CompositorObserver* observer) const {
   return observer_list_.HasObserver(observer);
 }
 
@@ -326,7 +326,8 @@ void Compositor::RemoveAnimationObserver(
   animation_observer_list_.RemoveObserver(observer);
 }
 
-bool Compositor::HasAnimationObserver(CompositorAnimationObserver* observer) {
+bool Compositor::HasAnimationObserver(
+    const CompositorAnimationObserver* observer) const {
   return animation_observer_list_.HasObserver(observer);
 }
 
diff --git a/ui/compositor/compositor.h b/ui/compositor/compositor.h
index a6520a2..a5dc5d0 100644
--- a/ui/compositor/compositor.h
+++ b/ui/compositor/compositor.h
@@ -216,11 +216,11 @@ class COMPOSITOR_EXPORT Compositor
   // observer to remove itself when it is done observing.
   void AddObserver(CompositorObserver* observer);
   void RemoveObserver(CompositorObserver* observer);
-  bool HasObserver(CompositorObserver* observer);
+  bool HasObserver(const CompositorObserver* observer) const;
 
   void AddAnimationObserver(CompositorAnimationObserver* observer);
   void RemoveAnimationObserver(CompositorAnimationObserver* observer);
-  bool HasAnimationObserver(CompositorAnimationObserver* observer);
+  bool HasAnimationObserver(const CompositorAnimationObserver* observer) const;
 
   // Creates a compositor lock. Returns NULL if it is not possible to lock at
   // this time (i.e. we're waiting to complete a previous unlock).
diff --git a/ui/views/widget/widget.cc b/ui/views/widget/widget.cc
index eecbc23..7f649c0 100644
--- a/ui/views/widget/widget.cc
+++ b/ui/views/widget/widget.cc
@@ -393,7 +393,7 @@ void Widget::RemoveObserver(WidgetObserver* observer) {
   observers_.RemoveObserver(observer);
 }
 
-bool Widget::HasObserver(WidgetObserver* observer) {
+bool Widget::HasObserver(const WidgetObserver* observer) const {
   return observers_.HasObserver(observer);
 }
 
@@ -405,7 +405,7 @@ void Widget::RemoveRemovalsObserver(WidgetRemovalsObserver* observer) {
   removals_observers_.RemoveObserver(observer);
 }
 
-bool Widget::HasRemovalsObserver(WidgetRemovalsObserver* observer) {
+bool Widget::HasRemovalsObserver(const WidgetRemovalsObserver* observer) const {
   return removals_observers_.HasObserver(observer);
 }
 
diff --git a/ui/views/widget/widget.h b/ui/views/widget/widget.h
index ac3e330..e208d5f 100644
--- a/ui/views/widget/widget.h
+++ b/ui/views/widget/widget.h
@@ -364,12 +364,12 @@ class VIEWS_EXPORT Widget : public internal::NativeWidgetDelegate,
   // Add/remove observer.
   void AddObserver(WidgetObserver* observer);
   void RemoveObserver(WidgetObserver* observer);
-  bool HasObserver(WidgetObserver* observer);
+  bool HasObserver(const WidgetObserver* observer) const;
 
   // Add/remove removals observer.
   void AddRemovalsObserver(WidgetRemovalsObserver* observer);
   void RemoveRemovalsObserver(WidgetRemovalsObserver* observer);
-  bool HasRemovalsObserver(WidgetRemovalsObserver* observer);
+  bool HasRemovalsObserver(const WidgetRemovalsObserver* observer) const;
 
   // Returns the accelerator given a command id. Returns false if there is
   // no accelerator associated with a given id, which is a common condition.
diff --git a/ui/wm/core/user_activity_detector.cc b/ui/wm/core/user_activity_detector.cc
index 6b06743..a9f85e8 100644
--- a/ui/wm/core/user_activity_detector.cc
+++ b/ui/wm/core/user_activity_detector.cc
@@ -59,7 +59,8 @@ UserActivityDetector* UserActivityDetector::Get() {
   return g_instance;
 }
 
-bool UserActivityDetector::HasObserver(UserActivityObserver* observer) const {
+bool UserActivityDetector::HasObserver(
+    const UserActivityObserver* observer) const {
   return observers_.HasObserver(observer);
 }
 
diff --git a/ui/wm/core/user_activity_detector.h b/ui/wm/core/user_activity_detector.h
index 13e290e..55ffc24 100644
--- a/ui/wm/core/user_activity_detector.h
+++ b/ui/wm/core/user_activity_detector.h
@@ -36,7 +36,7 @@ class WM_EXPORT UserActivityDetector : public ui::EventHandler {
 
   void set_now_for_test(base::TimeTicks now) { now_for_test_ = now; }
 
-  bool HasObserver(UserActivityObserver* observer) const;
+  bool HasObserver(const UserActivityObserver* observer) const;
   void AddObserver(UserActivityObserver* observer);
   void RemoveObserver(UserActivityObserver* observer);