[web] Code cleanup (#27815)

lib/web_ui/lib/src/engine.dart

@@ -330,9 +330,12 @@ export 'engine/window.dart';
 /// Keep these in sync with the same constants on the framework-side under foundation/constants.dart.
 const bool kReleaseMode =
     bool.fromEnvironment('dart.vm.product', defaultValue: false);
+/// A constant that is true if the application was compiled in profile mode.
 const bool kProfileMode =
     bool.fromEnvironment('dart.vm.profile', defaultValue: false);
+/// A constant that is true if the application was compiled in debug mode.
 const bool kDebugMode = !kReleaseMode && !kProfileMode;
+/// Returns mode of the app is running in as a string.
 String get buildMode => kReleaseMode
     ? 'release'
     : kProfileMode
@@ -454,6 +457,8 @@ void _addUrlStrategyListener() {
   });
 }
 
+/// Sanitizer used to convert const svg filter and clippath snippets to
+/// SvgElement without sanitization.
 class NullTreeSanitizer implements html.NodeTreeSanitizer {
   @override
   void sanitizeTree(html.Node node) {}

lib/web_ui/lib/src/engine/alarm_clock.dart

@@ -18,6 +18,8 @@ typedef TimestampFunction = DateTime Function();
 ///
 /// https://developer.mozilla.org/en-US/docs/Web/API/WindowOrWorkerGlobalScope/setTimeout#Notes
 class AlarmClock {
+
+  /// Initializes Alarmclock with a closure that gets called with a timestamp.
   AlarmClock(TimestampFunction timestampFunction)
       : _timestampFunction = timestampFunction;
 

lib/web_ui/lib/src/engine/assets.dart

@@ -19,6 +19,7 @@ class AssetManager {
   /// The directory containing the assets.
   final String assetsDir;
 
+  /// Initializes [AssetManager] with path to assets relative to baseUrl.
   const AssetManager({this.assetsDir = _defaultAssetsDir});
 
   String? get _baseUrl {
@@ -53,6 +54,7 @@ class AssetManager {
     return Uri.encodeFull((_baseUrl ?? '') + '$assetsDir/$asset');
   }
 
+  /// Loads an asset using an [html.HttpRequest] and returns data as [ByteData].
   Future<ByteData> load(String asset) async {
     final String url = getAssetUrl(asset);
     try {
@@ -77,10 +79,14 @@ class AssetManager {
   }
 }
 
+/// Thrown to indicate http failure during asset loading.
 class AssetManagerException implements Exception {
+  /// Http request url for asset.
   final String url;
+  /// Http status of of response.
   final int httpStatus;
 
+  /// Initializes exception with request url and http status.
   AssetManagerException(this.url, this.httpStatus);
 
   @override
@@ -89,8 +95,11 @@ class AssetManagerException implements Exception {
 
 /// An asset manager that gives fake empty responses for assets.
 class WebOnlyMockAssetManager implements AssetManager {
+  /// Mock asset directory relative to base url.
   String defaultAssetsDir = '';
+  /// Mock empty asset manifest.
   String defaultAssetManifest = '{}';
+  /// Mock font manifest overridable for unit testing.
   String defaultFontManifest = '''
   [
    {

lib/web_ui/lib/src/engine/browser_detection.dart

@@ -33,9 +33,9 @@ enum BrowserEngine {
 
 /// html webgl version qualifier constants.
 abstract class WebGLVersion {
-  // WebGL 1.0 is based on OpenGL ES 2.0 / GLSL 1.00
+  /// WebGL 1.0 is based on OpenGL ES 2.0 / GLSL 1.00
   static const int webgl1 = 1;
-  // WebGL 2.0 is based on OpenGL ES 3.0 / GLSL 3.00
+  /// WebGL 2.0 is based on OpenGL ES 3.0 / GLSL 3.00
   static const int webgl2 = 2;
 }
 
@@ -78,6 +78,9 @@ bool _isSamsungBrowser(String agent) {
   return exp.hasMatch(agent.toUpperCase());
 }
 
+/// Detects browser engine for a given vendor and agent string.
+///
+/// Used for testing this library.
 @visibleForTesting
 BrowserEngine detectBrowserEngineByVendorAgent(String vendor, String agent) {
   if (vendor == 'Google Inc.') {
@@ -149,6 +152,7 @@ OperatingSystem get operatingSystem {
 /// This is intended to be used for testing and debugging only.
 OperatingSystem? debugOperatingSystemOverride;
 
+/// Detects operating system using platform and UA used for unit testing.
 @visibleForTesting
 OperatingSystem detectOperatingSystem({
   String? overridePlatform,