Add `SDImageCacheScaleDownLargeImages` to allow cache to scale down large images if need

@@ -33,7 +33,12 @@ typedef NS_OPTIONS(NSUInteger, SDImageCacheOptions) {
     /**
      * By default, we query the memory cache synchronously, disk cache asynchronously. This mask can force to query disk cache synchronously.
      */
-    SDImageCacheQueryDiskSync = 1 << 1
+    SDImageCacheQueryDiskSync = 1 << 1,
+    /**
+     * By default, images are decoded respecting their original size. On iOS, this flag will scale down the
+     * images to a size compatible with the constrained memory of devices.
+     */
+    SDImageCacheScaleDownLargeImages = 1 << 2
 };
 
 typedef void(^SDCacheQueryCompletedBlock)(UIImage * _Nullable image, NSData * _Nullable data, SDImageCacheType cacheType);

@@ -440,11 +440,16 @@ FOUNDATION_STATIC_INLINE NSUInteger SDCacheCostForImage(UIImage *image) {
 }
 
 - (nullable UIImage *)diskImageForKey:(nullable NSString *)key data:(nullable NSData *)data {
+    return [self diskImageForKey:key data:data options:0];
+}
+
+- (nullable UIImage *)diskImageForKey:(nullable NSString *)key data:(nullable NSData *)data options:(SDImageCacheOptions)options {
     if (data) {
         UIImage *image = [[SDWebImageCodersManager sharedInstance] decodedImageWithData:data];
         image = [self scaledImageForKey:key image:image];
         if (self.config.shouldDecompressImages) {
-            image = [[SDWebImageCodersManager sharedInstance] decompressedImageWithImage:image data:&data options:@{SDWebImageCoderScaleDownLargeImagesKey: @(NO)}];
+            BOOL shouldScaleDown = options & SDImageCacheScaleDownLargeImages;
+            image = [[SDWebImageCodersManager sharedInstance] decompressedImageWithImage:image data:&data options:@{SDWebImageCoderScaleDownLargeImagesKey: @(shouldScaleDown)}];
         }
         return image;
     } else {
@@ -495,7 +500,7 @@ FOUNDATION_STATIC_INLINE NSUInteger SDCacheCostForImage(UIImage *image) {
                 cacheType = SDImageCacheTypeMemory;
             } else if (diskData) {
                 // decode image data only if in-memory cache missed
-                diskImage = [self diskImageForKey:key data:diskData];
+                diskImage = [self diskImageForKey:key data:diskData options:options];
                 if (diskImage && self.config.shouldCacheImagesInMemory) {
                     NSUInteger cost = SDCacheCostForImage(diskImage);
                     [self.memCache setObject:diskImage forKey:key cost:cost];

@@ -148,6 +148,7 @@
     SDImageCacheOptions cacheOptions = 0;
     if (options & SDWebImageQueryDataWhenInMemory) cacheOptions |= SDImageCacheQueryDataWhenInMemory;
     if (options & SDWebImageQueryDiskSync) cacheOptions |= SDImageCacheQueryDiskSync;
+    if (options & SDWebImageScaleDownLargeImages) cacheOptions |= SDImageCacheScaleDownLargeImages;
     
     __weak SDWebImageCombinedOperation *weakOperation = operation;
     operation.cacheOperation = [self.imageCache queryCacheOperationForKey:key options:cacheOptions done:^(UIImage *cachedImage, NSData *cachedData, SDImageCacheType cacheType) {