add scroll_aware

com.unity.uiwidgets/Runtime/widgets/scroll_aware_image_provider.cs

+using System;
+using Unity.UIWidgets.animation;
+using Unity.UIWidgets.async2;
+using Unity.UIWidgets.foundation;
+using Unity.UIWidgets.gestures;
+using Unity.UIWidgets.painting;
+using Unity.UIWidgets.physics;
+using Unity.UIWidgets.scheduler2;
+using Unity.UIWidgets.ui;
+using UnityEngine;
+
+namespace Unity.UIWidgets.widgets {
+    public class ScrollAwareImageProvider<T> : ImageProvider<T> {
+        public ScrollAwareImageProvider(
+            DisposableBuildContext context = null,
+            ImageProvider<T> imageProvider = null
+        ) {
+            D.assert(context != null);
+            D.assert(imageProvider != null);
+            this.context = context;
+            this.imageProvider = imageProvider;
+        }
+        public readonly DisposableBuildContext context;
+
+        public readonly ImageProvider<T> imageProvider;
+        public override void resolveStreamForKey(
+            ImageConfiguration configuration, 
+            ImageStream stream, T key,
+            ImageErrorListener handleError) {
+   
+            if (stream.completer != null || PaintingBinding.instance.imageCache.containsKey(key)) {
+              imageProvider.resolveStreamForKey(configuration, stream, key, handleError);
+              return;
+            }
+          
+            if (context.context == null) {
+              return;
+            }
+            
+            if (Scrollable.recommendDeferredLoadingForContext(context.context)) {
+                SchedulerBinding.instance.scheduleFrameCallback((_)=> {
+                  async_.scheduleMicrotask(
+                      () => {
+                          resolveStreamForKey(configuration, stream, key, handleError);
+                          return null;
+                      }
+                      
+                  );
+                });
+                return;
+            }
+          
+            imageProvider.resolveStreamForKey(configuration, stream, key, handleError); 
+        }
+        public override ImageStreamCompleter load(T key, DecoderCallback decode) => imageProvider.load(key, decode);
+        public override Future<T> obtainKey(ImageConfiguration configuration) => imageProvider.obtainKey(configuration);
+    }
+
+}