Log when RCTImageView reloads and when assets are scaled

Summary: This sort of logging helped me identify issues with reloading images too frequently (and for trivial reasons), so leaving it in might be useful for future optimization work, or for anyone building apps using these components.

@​public

Reviewed By: @alexeylang

Differential Revision: D2475613

Author: jspahrsummers

Libraries/CameraRoll/RCTAssetsLibraryImageLoader.m

@@ -69,6 +69,21 @@ - (RCTImageLoaderCancellationBlock)loadImageForURL:(NSURL *)imageURL size:(CGSiz
           BOOL useMaximumSize = CGSizeEqualToSize(size, CGSizeZero);
           ALAssetRepresentation *representation = [asset defaultRepresentation];
 
+          #if RCT_DEV
+          CGSize sizeBeingLoaded = size;
+          if (useMaximumSize) {
+            CGSize pointSize = representation.dimensions;
+            sizeBeingLoaded = CGSizeMake(pointSize.width * representation.scale, pointSize.height * representation.scale);
+          }
+
+          CGSize screenSize = UIScreen.mainScreen.nativeBounds.size;
+          CGFloat maximumPixelDimension = fmax(screenSize.width, screenSize.height);
+
+          if (sizeBeingLoaded.width > maximumPixelDimension || sizeBeingLoaded.height > maximumPixelDimension) {
+            RCTLogInfo(@"[PERF ASSETS] Loading %@ at size %@, which is larger than screen size %@", representation.filename, NSStringFromCGSize(sizeBeingLoaded), NSStringFromCGSize(screenSize));
+          }
+          #endif
+
           UIImage *image;
           NSError *error = nil;
           if (useMaximumSize) {

Libraries/Image/RCTImageView.m

@@ -218,6 +218,8 @@ - (void)reactSetFrame:(CGRect)frame
 
     if (RCTShouldReloadImageForSizeChange(imageSize, idealSize)) {
       if (RCTShouldReloadImageForSizeChange(_targetSize, idealSize)) {
+        RCTLogInfo(@"[PERF IMAGEVIEW] Reloading image %@ as size %@", _src, NSStringFromCGSize(idealSize));
+
         // If the existing image or an image being loaded are not the right size, reload the asset in case there is a
         // better size available.
         _targetSize = idealSize;