[web] Implement tilemode for gradient shaders.

lib/web_ui/dev/goldens_lock.yaml

@@ -1,2 +1,2 @@
 repository: https://github.com/flutter/goldens.git
-revision: 67f22ef933be27ba2be8b27df1b71b2c69eb86e5
+revision: 06e0333b8371965dce5dc05e140e6dfb454f33fa

lib/web_ui/lib/src/engine/canvaskit/shader.dart

@@ -66,7 +66,7 @@ class CkGradientLinear extends CkShader implements ui.Gradient {
         assert(_offsetIsValid(to)),
         assert(colors != null), // ignore: unnecessary_null_comparison
         assert(tileMode != null), // ignore: unnecessary_null_comparison
-        this.matrix4 = matrix == null ? null : _FastMatrix64(matrix) {
+        this.matrix4 = matrix {
     if (assertionsEnabled) {
       _validateColorStops(colors, colorStops);
     }
@@ -77,7 +77,7 @@ class CkGradientLinear extends CkShader implements ui.Gradient {
   final List<ui.Color> colors;
   final List<double>? colorStops;
   final ui.TileMode tileMode;
-  final _FastMatrix64? matrix4;
+  final Float64List? matrix4;
 
   @override
   SkShader createDefault() {

lib/web_ui/lib/src/engine/html/render_vertices.dart

@@ -126,7 +126,7 @@ class _WebGlRenderer implements _GlRenderer {
     final String fragmentShader = _writeVerticesFragmentShader();
     _GlContext gl = _GlContextCache.createGlContext(widthInPixels, heightInPixels)!;
 
-    _GlProgram glProgram = gl.useAndCacheProgram(vertexShader, fragmentShader)!;
+    _GlProgram glProgram = gl.useAndCacheProgram(vertexShader, fragmentShader);
 
     Object transformUniform = gl.getUniformLocation(glProgram.program,
         'u_ctransform');
@@ -487,7 +487,7 @@ class _GlContext {
           left, top, _widthInPixels, _heightInPixels]);
   }
 
-  _GlProgram? useAndCacheProgram(
+  _GlProgram useAndCacheProgram(
       String vertexShaderSource, String fragmentShaderSource) {
     String cacheKey = '$vertexShaderSource||$fragmentShaderSource';
     _GlProgram? cachedProgram = _programCache[cacheKey];