Mac: Make ScopedTypeRef require explicit constructors

device/bluetooth/test/bluetooth_test_mac.mm

Index: device/bluetooth/test/bluetooth_test_mac.mm
diff --git a/device/bluetooth/test/bluetooth_test_mac.mm b/device/bluetooth/test/bluetooth_test_mac.mm
index 4a27f3be741b9b46614d225762a8a071b70e8f58..903dc53b0b026e2c525b82e41e301df7ff51d7c3 100644
--- a/device/bluetooth/test/bluetooth_test_mac.mm
+++ b/device/bluetooth/test/bluetooth_test_mac.mm
@@ -41,7 +41,8 @@ explicit ScopedMockCentralManager(MockCentralManager* mock_central_manager) {
 
 namespace {
 
-NSDictionary* CreateAdvertisementData(NSString* name, NSArray* uuids) {
+scoped_nsobject<NSDictionary> CreateAdvertisementData(NSString* name,
+                                                      NSArray* uuids) {
   NSMutableDictionary* advertisement_data =
       [NSMutableDictionary dictionaryWithDictionary:@{
         CBAdvertisementDataLocalNameKey : name,
@@ -52,7 +53,7 @@ explicit ScopedMockCentralManager(MockCentralManager* mock_central_manager) {
     [advertisement_data setObject:uuids
                            forKey:CBAdvertisementDataServiceUUIDsKey];
   }
-  return [advertisement_data retain];
+  return scoped_nsobject<NSDictionary>([advertisement_data retain]);

[Reilly Grant (use Gerrit), 2016/06/01 01:05:15]

I believe this retain was and still is unnecessary.

[ccameron, 2016/06/01 01:59:31]

Yeah, I suspected. Removed.

[Eugene But (OOO till 7-30), 2016/06/01 05:12:06]

Wait... this retain is still necessary (and actually was necessary).
1.) |dictionaryWithDictionary:| returns autoreleased objects 
2.) scoped_nsobject takes ownership over |advertisement_data|
3.) scoped_nsobject releases |advertisement_data| on destruction
4.) autorelease pool releases |advertisement_data| when it's drained

So dropping |retain| will lead to a crash, unless I'm missing something.

[Reilly Grant (use Gerrit), 2016/06/01 15:34:42]

I only pretend to understand Objective-C memory management. The documentation
doesn't *say* that it returns an autoreleased object but that makes sense.

[Eugene But (OOO till 7-30), 2016/06/01 15:58:35]

In Objective-C the method prefix tell if you are responsible for releasing the
object or not.
The following prefixes require callers to own the result:
- new
- alloc
- copy
- mutableCopy

https://developer.apple.com/library/mac/documentation/Cocoa/Conceptual/Memory...

[jlebel, 2016/06/02 23:07:34]

And "create" when we are using functions. That's the way it works for
CoreFoundation.

[ccameron, 2016/06/02 23:11:18]

I've added a base::scoped_policy::RETAIN here.

 }
 
 }  // namespace
@@ -229,7 +230,7 @@ explicit ScopedMockCentralManager(MockCentralManager* mock_central_manager) {
       static_cast<BluetoothLowEnergyDeviceMac*>(device);
   CBPeripheral* peripheral = device_mac->GetPeripheral();
   MockCBPeripheral* peripheral_mock = ObjCCast<MockCBPeripheral>(peripheral);
-  scoped_nsobject<NSMutableArray> services = [[NSMutableArray alloc] init];
+  scoped_nsobject<NSMutableArray> services([[NSMutableArray alloc] init]);
   for (auto uuid : uuids) {
     CBUUID* cb_service_uuid = [CBUUID UUIDWithString:@(uuid.c_str())];
     [services addObject:cb_service_uuid];