Enable structured errors by default. (#72446)

* Enable structured errors by default.

packages/flutter/lib/src/widgets/widget_inspector.dart

@@ -960,7 +960,15 @@ mixin WidgetInspectorService {
   /// Structured errors provide semantic information that can be used by IDEs
   /// to enhance the display of errors with rich formatting.
   bool isStructuredErrorsEnabled() {
-    return const bool.fromEnvironment('flutter.inspector.structuredErrors');
+    // This is a debug mode only feature and will default to false for
+    // profile mode.
+    bool enabled = false;
+    assert(() {
+      // TODO(kenz): add support for structured errors on the web.
+      enabled = const bool.fromEnvironment('flutter.inspector.structuredErrors', defaultValue: !kIsWeb);
+      return true;
+    }());
+    return enabled;
   }
 
   /// Called to register service extensions.

packages/flutter/test/widgets/widget_inspector_structure_error_test.dart

@@ -56,14 +56,14 @@ class StructureErrorTestWidgetInspectorService extends Object with WidgetInspect
     final StructureErrorTestWidgetInspectorService service = StructureErrorTestWidgetInspectorService();
     WidgetInspectorService.instance = service;
 
-    test('ext.flutter.inspector.structuredErrors still report error to original on error', () async {
+    test('ext.flutter.inspector.structuredErrors reports error to _structuredExceptionHandler on error', () async {
       final FlutterExceptionHandler? oldHandler = FlutterError.onError;
 
-      late FlutterErrorDetails actualError;
+      bool usingNewHandler = false;
       // Creates a spy onError. This spy needs to be set before widgets binding
       // initializes.
       FlutterError.onError = (FlutterErrorDetails details) {
-        actualError = details;
+        usingNewHandler = true;
       };
 
       WidgetsFlutterBinding.ensureInitialized();
@@ -81,8 +81,13 @@ class StructureErrorTestWidgetInspectorService extends Object with WidgetInspect
         );
         FlutterError.reportError(expectedError);
 
-        // Validates the spy still received an error.
-        expect(actualError, expectedError);
+        // For non-web apps, this validates the new handler did not receive an
+        // error because `FlutterError.onError` was set to
+        // `WidgetInspectorService._structuredExceptionHandler` when service
+        // extensions were initialized. For web apps, the new handler should
+        // have received an error because structured errors are disabled by
+        // default on the web.
+        expect(usingNewHandler, equals(kIsWeb));
       } finally {
         FlutterError.onError = oldHandler;
       }