Fix lint warnings across web_ui, add missing browserEngine case in text field.

lib/web_ui/dev/browser.dart

@@ -12,7 +12,7 @@ import 'package:typed_data/typed_buffers.dart';
 
 import 'package:test_api/src/utils.dart';
 
-import 'common.dart'; // ignore: implementation_imports
+import 'common.dart'; // ignore: unused_import
 
 /// An interface for running browser instances.
 ///

lib/web_ui/lib/src/engine/compositor/embedded_views.dart

@@ -472,6 +472,8 @@ class Mutator {
         return matrix == typedOther.matrix;
       case MutatorType.opacity:
         return alpha == typedOther.alpha;
+      default:
+        return false;
     }
   }
 

lib/web_ui/lib/src/engine/compositor/layer_scene_builder.dart

@@ -17,7 +17,6 @@ class LayerScene implements ui.Scene {
   @override
   Future<ui.Image> toImage(int width, int height) => null;
 
-  @override
   html.Element get webOnlyRootElement => null;
 }
 

lib/web_ui/lib/src/engine/compositor/surface.dart

@@ -52,7 +52,7 @@ class Surface {
 
     SubmitCallback submitCallback =
         (SurfaceFrame surfaceFrame, SkCanvas canvas) {
-      _presentSurface(canvas);
+      return _presentSurface(canvas);
     };
 
     return SurfaceFrame(surface, submitCallback);

lib/web_ui/lib/src/engine/compositor/text.dart

@@ -285,6 +285,7 @@ Map<String, js.JsObject> toSkFontStyle(
         break;
     }
   }
+  return style;
 }
 
 class SkParagraph implements ui.Paragraph {

lib/web_ui/lib/src/engine/semantics/text_field.dart

@@ -62,6 +62,7 @@ class TextField extends RoleManager {
       case BrowserEngine.blink:
       case BrowserEngine.edge:
       case BrowserEngine.firefox:
+      case BrowserEngine.ie11:
       case BrowserEngine.unknown:
         _initializeForBlink();
         break;

lib/web_ui/lib/src/engine/surface/painting.dart

@@ -20,8 +20,6 @@ class SurfacePaint implements ui.Paint {
     _paintData.blendMode = value;
   }
 
-  ui.BlendMode _blendMode;
-
   @override
   ui.PaintingStyle get style => _paintData.style ?? ui.PaintingStyle.fill;
 
@@ -102,9 +100,6 @@ class SurfacePaint implements ui.Paint {
   @override
   set invertColors(bool value) {}
 
-  @override
-  ui.Color _color = _defaultPaintColor;
-
   static const ui.Color _defaultPaintColor = ui.Color(0xFF000000);
 
   @override

lib/web_ui/lib/src/ui/canvas.dart

@@ -61,9 +61,9 @@ enum VertexMode {
 class Vertices {
   final VertexMode _mode;
   final Float32List _positions;
-  final Float32List _textureCoordinates;
+  final Float32List _textureCoordinates; // ignore: unused_field
   final Int32List _colors;
-  final Uint16List _indices;
+  final Uint16List _indices; // ignore: unused_field
 
   Vertices._(
     VertexMode mode,
@@ -1157,21 +1157,18 @@ class RawRecordingCanvas extends engine.BitmapCanvas
     clear();
   }
 
-  @override
   engine.RecordingCanvas beginRecording(Rect bounds) =>
       throw UnsupportedError('');
+
   @override
   Picture endRecording() => throw UnsupportedError('');
 
-  @override
-  engine.RecordingCanvas _canvas;
+  engine.RecordingCanvas _canvas; // ignore: unused_field
 
-  @override
-  bool _isRecording = true;
+  bool _isRecording = true; // ignore: unused_field
 
   @override
   bool get isRecording => true;
 
-  @override
   Rect cullRect;
 }

lib/web_ui/lib/src/ui/natives.dart

@@ -5,6 +5,7 @@
 part of ui;
 
 // Corelib 'print' implementation.
+// ignore: unused_element
 void _print(dynamic arg) {
   _Logger._printString(arg.toString());
 }

lib/web_ui/lib/src/ui/window.dart

@@ -778,7 +778,7 @@ abstract class Window {
   /// no later frames to batch.
   TimingsCallback get onReportTimings => _onReportTimings;
   TimingsCallback _onReportTimings;
-  Zone _onReportTimingsZone;
+  Zone _onReportTimingsZone; // ignore: unused_field
   set onReportTimings(TimingsCallback callback) {
     _onReportTimings = callback;
   }

lib/web_ui/test/engine/pointer_binding_test.dart

@@ -3,7 +3,6 @@
 // found in the LICENSE file.
 
 import 'dart:html' as html;
-import 'dart:typed_data';
 
 import 'package:ui/src/engine.dart';
 import 'package:ui/ui.dart' as ui;

lib/web_ui/test/golden_tests/engine/canvas_blend_golden_test.dart

@@ -3,7 +3,6 @@
 // found in the LICENSE file.
 
 import 'dart:html' as html;
-import 'dart:math' as math;
 import 'dart:js_util' as js_util;
 
 import 'package:ui/ui.dart' hide TextStyle;
@@ -16,7 +15,6 @@ void main() async {
   const double screenWidth = 600.0;
   const double screenHeight = 800.0;
   const Rect screenRect = Rect.fromLTWH(0, 0, screenWidth, screenHeight);
-  final Paint testPaint = Paint()..color = const Color(0xFFFF0000);
 
   // Commit a recording canvas to a bitmap, and compare with the expected
   Future<void> _checkScreenshot(RecordingCanvas rc, String fileName,

lib/web_ui/test/golden_tests/engine/canvas_draw_image_golden_test.dart

@@ -16,7 +16,6 @@ void main() async {
   const double screenWidth = 600.0;
   const double screenHeight = 800.0;
   const Rect screenRect = Rect.fromLTWH(0, 0, screenWidth, screenHeight);
-  final Paint testPaint = Paint()..color = const Color(0xFFFF0000);
 
   // Commit a recording canvas to a bitmap, and compare with the expected
   Future<void> _checkScreenshot(RecordingCanvas rc, String fileName,

lib/web_ui/test/golden_tests/engine/compositing_golden_test.dart

@@ -480,7 +480,7 @@ void _testCullRectComputation() {
 
     await matchGoldenFile('compositing_3d_rotate1.png', region: region);
 
-    final PersistedStandardPicture picture = enumeratePictures().single;
+    final PersistedStandardPicture picture = enumeratePictures().single; // ignore: unused_local_variable
     // TODO(https://github.com/flutter/flutter/issues/40395):
     //   Needs ability to set iframe to 500,100 size. Current screen seems to be 500,500.
     // expect(

lib/web_ui/test/golden_tests/engine/draw_vertices_golden_test.dart

@@ -72,6 +72,7 @@ void main() async {
   test('Should draw black hairline triangles when colors array is null'
       ' and Paint() has no color.',
           () async {
+    // ignore: unused_local_variable
     final Int32List colors = Int32List.fromList(<int>[
         0xFFFF0000, 0xFF00FF00, 0xFF0000FF,
         0xFFFF0000, 0xFF00FF00, 0xFF0000FF,