No image shader caching in default shader warm-up (#29179)

* No image shader caching in default shader warm-up

It turns out that no matter how small the image is, too much memory will
be used. Hence remove the image shader caching and let the client
implement itself based on needs.

Fixes https://github.com/flutter/flutter/issues/29172

* Fix

packages/flutter/lib/src/painting/shader_warm_up.dart

@@ -4,7 +4,6 @@
 
 import 'dart:async';
 import 'dart:developer';
-import 'dart:typed_data';
 import 'dart:ui' as ui;
 
 import 'package:flutter/foundation.dart';
@@ -106,7 +105,7 @@ class DefaultShaderWarmUp extends ShaderWarmUp {
   /// Trigger common draw operations on a canvas to warm up GPU shader
   /// compilation cache.
   @override
-  Future<void> warmUpOnCanvas(ui.Canvas canvas) {
+  Future<void> warmUpOnCanvas(ui.Canvas canvas) async {
     final ui.RRect rrect = ui.RRect.fromLTRBXY(20.0, 20.0, 60.0, 60.0, 10.0, 10.0);
     final ui.Path rrectPath = ui.Path()..addRRect(rrect);
 
@@ -181,30 +180,5 @@ class DefaultShaderWarmUp extends ShaderWarmUp {
     final ui.Paragraph paragraph = paragraphBuilder.build()
       ..layout(const ui.ParagraphConstraints(width: 60.0));
     canvas.drawParagraph(paragraph, const ui.Offset(20.0, 20.0));
-
-    // Construct an image for drawImage related operations
-    const int imageWidth = 10;
-    const int imageHeight = 10;
-    final Uint8List pixels = Uint8List.fromList(List<int>.generate(
-      imageWidth * imageHeight * 4,
-          (int i) => i % 4 < 2 ? 0x00 : 0xFF,  // opaque blue
-    ));
-
-    final Completer<void> completer = Completer<void>();
-    ui.decodeImageFromPixels(pixels, imageWidth, imageHeight, ui.PixelFormat.rgba8888, (ui.Image image) {
-      // Warm up image shaders
-      canvas.translate(0.0, 80.0);
-      canvas.save();
-      final ui.Rect srcRect = ui.Rect.fromLTWH(0.0, 0.0, image.width.toDouble(), image.height.toDouble());
-      canvas.drawImage(image, const ui.Offset(20.0, 20.0), ui.Paint());
-      canvas.translate(80.0, 0.0);
-      canvas.drawImageRect(image, srcRect, ui.Rect.fromLTWH(20.0, 20.0, imageWidth * 0.6, imageWidth * 0.6), paints[0]);
-      canvas.translate(80.0, 0.0);
-      canvas.drawImageRect(image, srcRect, ui.Rect.fromLTWH(10.0, 10.0, imageWidth * 1.5, imageWidth * 1.5), paints[0]);
-      canvas.restore();
-      completer.complete();
-    });
-
-    return completer.future;
   }
 }