Put download token init internal

SDWebImage/SDWebImageDownloader.h

@@ -91,8 +91,6 @@ FOUNDATION_EXPORT NSString * _Nonnull const SDWebImageDownloadStopNotification;
 typedef SDImageLoaderProgressBlock SDWebImageDownloaderProgressBlock;
 typedef SDImageLoaderCompletedBlock SDWebImageDownloaderCompletedBlock;
 
-@protocol SDWebImageDownloaderOperation;
-
 /**
  *  A token associated with each download. Can be used to cancel a download
  */
@@ -118,11 +116,6 @@ typedef SDImageLoaderCompletedBlock SDWebImageDownloaderCompletedBlock;
  */
 @property (nonatomic, strong, nullable, readonly) NSURLResponse *response;
 
-/**
- Init download token with downloadOperation.
- */
-- (nonnull instancetype)initWithDownloadOperation:(nullable NSOperation<SDWebImageDownloaderOperation> *)downloadOperation;
-
 @end
 
 

SDWebImage/SDWebImageDownloader.m

@@ -23,6 +23,10 @@ static void * SDWebImageDownloaderContext = &SDWebImageDownloaderContext;
 @property (nonatomic, weak, nullable) SDWebImageDownloader *downloader;
 @property (nonatomic, assign, getter=isCancelled) BOOL cancelled;
 
+- (nonnull instancetype)init NS_UNAVAILABLE;
++ (nonnull instancetype)new  NS_UNAVAILABLE;
+- (nonnull instancetype)initWithDownloadOperation:(nullable NSOperation<SDWebImageDownloaderOperation> *)downloadOperation NS_DESIGNATED_INITIALIZER;
+
 @end
 
 @interface SDWebImageDownloader () <NSURLSessionTaskDelegate, NSURLSessionDataDelegate>
@@ -431,10 +435,6 @@ didReceiveResponse:(NSURLResponse *)response
     [[NSNotificationCenter defaultCenter] removeObserver:self name:SDWebImageDownloadReceiveResponseNotification object:nil];
 }
 
-- (instancetype)init {
-    return [self initWithDownloadOperation:nil];
-}
-
 - (instancetype)initWithDownloadOperation:(NSOperation<SDWebImageDownloaderOperation> *)downloadOperation {
     self = [super init];
     if (self) {