Make the device::HidService destructor protected.

This prevents anything other than device::HidService::Destroyer from
calling the destructor. For example, scoped_ptr, as was the case in
HidConnectionTest.

BUG=

Review URL: https://codereview.chromium.org/542153004

Cr-Commit-Position: refs/heads/master@{#293623}

device/hid/hid_connection_unittest.cc

@@ -73,8 +73,7 @@ class HidConnectionTest : public testing::Test {
     if (!UsbTestGadget::IsTestEnabled()) return;
 
     message_loop_.reset(new base::MessageLoopForIO());
-    service_.reset(HidService::GetInstance(
-        message_loop_->message_loop_proxy()));
+    service_ = HidService::GetInstance(message_loop_->message_loop_proxy());
     ASSERT_TRUE(service_);
 
     test_gadget_ = UsbTestGadget::Claim();
@@ -119,7 +118,7 @@ class HidConnectionTest : public testing::Test {
   }
 
   scoped_ptr<base::MessageLoopForIO> message_loop_;
-  scoped_ptr<HidService> service_;
+  HidService* service_;
   scoped_ptr<UsbTestGadget> test_gadget_;
   HidDeviceId device_id_;
 };

device/hid/hid_service.cc

@@ -25,11 +25,13 @@ namespace {
 
 HidService* g_service = NULL;
 
-class HidServiceDestroyer : public base::MessageLoop::DestructionObserver {
+}  // namespace
+
+class HidService::Destroyer : public base::MessageLoop::DestructionObserver {
  public:
-  explicit HidServiceDestroyer(HidService* hid_service)
+  explicit Destroyer(HidService* hid_service)
       : hid_service_(hid_service) {}
-  virtual ~HidServiceDestroyer() {}
+  virtual ~Destroyer() {}
 
  private:
   // base::MessageLoop::DestructionObserver implementation.
@@ -43,8 +45,6 @@ class HidServiceDestroyer : public base::MessageLoop::DestructionObserver {
   HidService* hid_service_;
 };
 
-}  // namespace
-
 HidService* HidService::GetInstance(
     scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner) {
   if (g_service == NULL) {
@@ -56,7 +56,7 @@ HidService* HidService::GetInstance(
     g_service = new HidServiceWin();
 #endif
     if (g_service != NULL) {
-      HidServiceDestroyer* destroyer = new HidServiceDestroyer(g_service);
+      Destroyer* destroyer = new Destroyer(g_service);
       base::MessageLoop::current()->AddDestructionObserver(destroyer);
     }
   }

device/hid/hid_service.h

@@ -23,8 +23,6 @@ class HidService {
   static HidService* GetInstance(
       scoped_refptr<base::SingleThreadTaskRunner> ui_task_runner);
 
-  virtual ~HidService();
-
   // Enumerates and returns a list of device identifiers.
   virtual void GetDevices(std::vector<HidDeviceInfo>* devices);
 
@@ -41,6 +39,7 @@ class HidService {
   typedef std::map<HidDeviceId, HidDeviceInfo> DeviceMap;
 
   HidService();
+  virtual ~HidService();
 
   void AddDevice(const HidDeviceInfo& info);
   void RemoveDevice(const HidDeviceId& device_id);
@@ -49,6 +48,8 @@ class HidService {
   base::ThreadChecker thread_checker_;
 
  private:
+  class Destroyer;
+
   DeviceMap devices_;
 
   DISALLOW_COPY_AND_ASSIGN(HidService);