Remove dart:html from more excerpt sources (#6394)

examples/misc/lib/library_tour/async/stream_web.dart

@@ -1,9 +1,9 @@
-import 'dart:html';
+import 'package:web/web.dart' as web;
 
 void miscDeclAnalyzedButNotTested() {
   {
     void submitData() {}
-    var submitButton = querySelector('#submitInfo')!;
+    var submitButton = web.document.querySelector('#submitInfo')!;
     // #docregion listen
     // Add an event handler to a button.
     submitButton.onClick.listen((e) {

examples/type_system/lib/common_fixes_analysis.dart

@@ -1,32 +1,32 @@
 // NOTE: Declarations in this file are analyzed but not tested.
 // ignore_for_file: unused_element, unused_local_variable, one_member_abstracts, use_super_parameters
-// ignore_for_file: prefer_function_declarations_over_variables, unused_field, strict_raw_type, deprecated_member_use
+// ignore_for_file: prefer_function_declarations_over_variables, unused_field, strict_raw_type
 
-import 'dart:html';
+import 'package:web/web.dart';
 
-// Include in this file only excerpts used to illustrate fixes to common problems.
+// Excerpts used to illustrate potential fixes to common type problems.
 void _samplesFromCommonProblemsPage() {
   final double x = 0;
   final double y = 0;
 
   {
     // #docregion canvas-undefined
-    var canvas = querySelector('canvas')!;
+    var canvas = document.querySelector('canvas')!;
     // ignore: stable, beta, dev, undefined_getter
     canvas.context2D.lineTo(x, y);
     // #enddocregion canvas-undefined
   }
 
   {
     // #docregion canvas-as
-    var canvas = querySelector('canvas') as CanvasElement;
+    var canvas = document.querySelector('canvas') as HTMLCanvasElement;
     canvas.context2D.lineTo(x, y);
     // #enddocregion canvas-as
   }
 
   {
     // #docregion canvas-dynamic
-    dynamic canvasOrImg = querySelector('canvas, img');
+    var canvasOrImg = document.querySelector('canvas, img') as dynamic;
     var width = canvasOrImg.width;
     // #enddocregion canvas-dynamic
   }

examples/type_system/pubspec.yaml

@@ -7,6 +7,7 @@ environment:
 
 dependencies:
   examples_util: {path: ../util}
+  web: ^1.1.0
 
 dev_dependencies:
   test: ^1.25.8

src/content/deprecated/sound-problems.md

@@ -99,7 +99,7 @@ In the following code, the analyzer complains that `context2D` is undefined:
 
 <?code-excerpt "lib/common_fixes_analysis.dart (canvas-undefined)" replace="/context2D/[!$&!]/g"?>
 ```dart tag=fails-sa
-var canvas = querySelector('canvas')!;
+var canvas = document.querySelector('canvas')!;
 canvas.[!context2D!].lineTo(x, y);
 ```
 
@@ -121,15 +121,15 @@ You can fix this error with an explicit downcast:
 
 <?code-excerpt "lib/common_fixes_analysis.dart (canvas-as)" replace="/as \w+/[!$&!]/g"?>
 ```dart tag=passes-sa
-var canvas = querySelector('canvas') [!as CanvasElement!];
+var canvas = document.querySelector('canvas') [!as HTMLCanvasElement!];
 canvas.context2D.lineTo(x, y);
 ```
 
-Otherwise, use `dynamic` in situations where you cannot use a single type:
+Otherwise, use `dynamic` in situations where you can't use a single type:
 
 <?code-excerpt "lib/common_fixes_analysis.dart (canvas-dynamic)" replace="/dynamic/[!$&!]/g"?>
 ```dart tag=passes-sa
-[!dynamic!] canvasOrImg = querySelector('canvas, img');
+var canvasOrImg = document.querySelector('canvas, img') as [!dynamic!];
 var width = canvasOrImg.width;
 ```