Flag to transform animated images

Using a new SDWebImageOptions flag: SDWebImageTransformAnimatedImage

@@ -74,7 +74,14 @@ typedef NS_OPTIONS(NSUInteger, SDWebImageOptions) {
      * By default, placeholder images are loaded while the image is loading. This flag will delay the loading
      * of the placeholder image until after the image has finished loading.
      */
-    SDWebImageDelayPlaceholder = 1 << 9
+    SDWebImageDelayPlaceholder = 1 << 9,
+
+    /**
+     * We usually don't call transformDownloadedImage delegate method on animated images,
+     * as most transformation code would mangle it.
+     * Use this flag to transform them anyway.
+     */
+    SDWebImageTransformAnimatedImage = 1 << 10,
 };
 
 typedef void(^SDWebImageCompletionBlock)(UIImage *image, NSError *error, SDImageCacheType cacheType, NSURL *imageURL);

@@ -204,8 +204,7 @@
                     if (options & SDWebImageRefreshCached && image && !downloadedImage) {
                         // Image refresh hit the NSURLCache cache, do not call the completion block
                     }
-                            // NOTE: We don't call transformDownloadedImage delegate method on animated images as most transformation code would mangle it
-                    else if (downloadedImage && !downloadedImage.images && [self.delegate respondsToSelector:@selector(imageManager:transformDownloadedImage:withURL:)]) {
+                    else if (downloadedImage && (!downloadedImage.images || (options & SDWebImageTransformAnimatedImage)) && [self.delegate respondsToSelector:@selector(imageManager:transformDownloadedImage:withURL:)]) {
                         dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_HIGH, 0), ^{
                             UIImage *transformedImage = [self.delegate imageManager:self transformDownloadedImage:downloadedImage withURL:url];