Find the target platform more accurately on the web. (#61587)

packages/flutter/lib/src/foundation/_platform_web.dart

@@ -7,9 +7,9 @@ import 'platform.dart' as platform;
 
 /// The dart:html implementation of [platform.defaultTargetPlatform].
 platform.TargetPlatform get defaultTargetPlatform {
-  // To getter a better guess at the targetPlatform we need to be able to
-  // reference the window, but that won't be available until we fix the
-  // platforms configuration for Flutter.
+  // To get a better guess at the targetPlatform we need to be able to reference
+  // the window, but that won't be available until we fix the platforms
+  // configuration for Flutter.
   platform.TargetPlatform result = _browserPlatform();
   if (platform.debugDefaultTargetPlatformOverride != null)
     result = platform.debugDefaultTargetPlatformOverride!;
@@ -21,10 +21,24 @@ platform.TargetPlatform _browserPlatform() {
   if (navigatorPlatform.startsWith('mac')) {
     return platform.TargetPlatform.macOS;
   }
+  if (navigatorPlatform.startsWith('win')) {
+    return platform.TargetPlatform.windows;
+  }
   if (navigatorPlatform.contains('iphone') ||
       navigatorPlatform.contains('ipad') ||
       navigatorPlatform.contains('ipod')) {
     return platform.TargetPlatform.iOS;
   }
+  if (navigatorPlatform.contains('android')) {
+    return platform.TargetPlatform.android;
+  }
+  // Since some phones can report a window.navigator.platform as Linux, fall
+  // back to use CSS to disambiguate Android vs Linux desktop. If the CSS
+  // indicates that a device has a "fine pointer" (mouse) as the primary
+  // pointing device, then we'll assume desktop linux, and otherwise we'll
+  // assume Android.
+  if (html.window.matchMedia('only screen and (pointer: fine)').matches) {
+    return platform.TargetPlatform.linux;
+  }
   return platform.TargetPlatform.android;
 }

packages/flutter/lib/src/foundation/platform.dart

@@ -23,9 +23,12 @@ import '_platform_io.dart'
 /// adaptations for iOS later). Tests can check iOS behavior by using the
 /// platform override APIs (such as [ThemeData.platform] in the material
 /// library) or by setting [debugDefaultTargetPlatformOverride].
+///
+/// Tests can also create specific platform tests by and adding a `variant:`
+/// argument to the test and using a [TargetPlatformVariant].
 //
-// When adding support for a new platform (e.g. Windows Phone, macOS), first
-// create a new value on the [TargetPlatform] enum, then add a rule for
+// When adding support for a new platform (e.g. Windows Phone, Rasberry Pi),
+// first create a new value on the [TargetPlatform] enum, then add a rule for
 // selecting that platform here.
 //
 // It would be incorrect to make a platform that isn't supported by
@@ -42,7 +45,7 @@ enum TargetPlatform {
   /// Android: <https://www.android.com/>
   android,
 
-  /// Fuchsia: <https://fuchsia.googlesource.com/>
+  /// Fuchsia: <https://fuchsia.dev/fuchsia-src/concepts>
   fuchsia,
 
   /// iOS: <https://www.apple.com/ios/>