Generalized image decoding and resizing logic

Summary:
public

Standardises the image decoding logic for all image sources, meaning we get the benefits of efficient downscaling of images from all sources, not just ALAssets.

Reviewed By: javache

Differential Revision: D2647083

fb-gh-sync-id: e41456f838e4c6ab709b1c1523f651a86ff6e623

Libraries/Image/RCTResizeMode.h

@@ -0,0 +1,22 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ */
+
+#import "RCTConvert.h"
+
+typedef NS_ENUM(NSInteger, RCTResizeMode) {
+  RCTResizeModeCover = UIViewContentModeScaleAspectFill,
+  RCTResizeModeContain = UIViewContentModeScaleAspectFit,
+  RCTResizeModeStretch = UIViewContentModeScaleToFill,
+};
+
+@interface RCTConvert(RCTResizeMode)
+
++ (RCTResizeMode)RCTResizeMode:(id)json;
+
+@end