fix(example): avoid building unsupported PerformanceOverlay on web platform

example/lib/pages/many_circles.dart

@@ -1,10 +1,12 @@
 import 'dart:math';
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_map/flutter_map.dart';
 import 'package:flutter_map_example/misc/tile_providers.dart';
 import 'package:flutter_map_example/widgets/drawer/menu_drawer.dart';
 import 'package:flutter_map_example/widgets/number_of_items_slider.dart';
+import 'package:flutter_map_example/widgets/show_no_web_perf_overlay_snackbar.dart';
 import 'package:latlong2/latlong.dart';
 
 const _maxCirclesCount = 20000;
@@ -33,6 +35,9 @@ class ManyCirclesPageState extends State<ManyCirclesPage> {
   @override
   void initState() {
     super.initState();
+
+    showNoWebPerfOverlaySnackbar(context);
+
     Future.microtask(() {
       final r = Random();
       for (var x = 0; x < _maxCirclesCount; x++) {
@@ -86,12 +91,13 @@ class ManyCirclesPageState extends State<ManyCirclesPage> {
               onChangedNumber: (v) => setState(() => numOfCircles = v),
             ),
           ),
-          Positioned(
-            bottom: 16,
-            left: 0,
-            right: 0,
-            child: PerformanceOverlay.allEnabled(),
-          ),
+          if (!kIsWeb)
+            Positioned(
+              bottom: 16,
+              left: 0,
+              right: 0,
+              child: PerformanceOverlay.allEnabled(),
+            ),
         ],
       ),
     );

example/lib/pages/many_markers.dart

@@ -1,10 +1,12 @@
 import 'dart:math';
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_map/flutter_map.dart';
 import 'package:flutter_map_example/misc/tile_providers.dart';
 import 'package:flutter_map_example/widgets/drawer/menu_drawer.dart';
 import 'package:flutter_map_example/widgets/number_of_items_slider.dart';
+import 'package:flutter_map_example/widgets/show_no_web_perf_overlay_snackbar.dart';
 import 'package:latlong2/latlong.dart';
 
 const _maxMarkersCount = 20000;
@@ -33,6 +35,9 @@ class ManyMarkersPageState extends State<ManyMarkersPage> {
   @override
   void initState() {
     super.initState();
+
+    showNoWebPerfOverlaySnackbar(context);
+
     Future.microtask(() {
       final r = Random();
       for (var x = 0; x < _maxMarkersCount; x++) {
@@ -87,12 +92,13 @@ class ManyMarkersPageState extends State<ManyMarkersPage> {
               onChangedNumber: (v) => setState(() => numOfMarkers = v),
             ),
           ),
-          Positioned(
-            bottom: 16,
-            left: 0,
-            right: 0,
-            child: PerformanceOverlay.allEnabled(),
-          ),
+          if (!kIsWeb)
+            Positioned(
+              bottom: 16,
+              left: 0,
+              right: 0,
+              child: PerformanceOverlay.allEnabled(),
+            ),
         ],
       ),
     );

example/lib/pages/polygon_perf_stress.dart

@@ -4,6 +4,7 @@ import 'package:flutter/services.dart';
 import 'package:flutter_map/flutter_map.dart';
 import 'package:flutter_map_example/misc/tile_providers.dart';
 import 'package:flutter_map_example/widgets/drawer/menu_drawer.dart';
+import 'package:flutter_map_example/widgets/show_no_web_perf_overlay_snackbar.dart';
 import 'package:flutter_map_example/widgets/simplification_tolerance_slider.dart';
 import 'package:flutter_map_geojson/flutter_map_geojson.dart';
 import 'package:latlong2/latlong.dart';
@@ -29,6 +30,12 @@ class _PolygonPerfStressPageState extends State<PolygonPerfStressPage> {
             ),
           );
 
+  @override
+  void initState() {
+    super.initState();
+    showNoWebPerfOverlaySnackbar(context);
+  }
+
   @override
   void dispose() {
     geoJsonLoader.ignore();
@@ -82,12 +89,13 @@ class _PolygonPerfStressPageState extends State<PolygonPerfStressPage> {
                   setState(() => simplificationTolerance = v),
             ),
           ),
-          Positioned(
-            bottom: 16,
-            left: 0,
-            right: 0,
-            child: PerformanceOverlay.allEnabled(),
-          ),
+          if (!kIsWeb)
+            Positioned(
+              bottom: 16,
+              left: 0,
+              right: 0,
+              child: PerformanceOverlay.allEnabled(),
+            ),
         ],
       ),
     );

example/lib/pages/polyline_perf_stress.dart

@@ -1,9 +1,11 @@
 import 'dart:math';
 
+import 'package:flutter/foundation.dart';
 import 'package:flutter/material.dart';
 import 'package:flutter_map/flutter_map.dart';
 import 'package:flutter_map_example/misc/tile_providers.dart';
 import 'package:flutter_map_example/widgets/drawer/menu_drawer.dart';
+import 'package:flutter_map_example/widgets/show_no_web_perf_overlay_snackbar.dart';
 import 'package:flutter_map_example/widgets/simplification_tolerance_slider.dart';
 import 'package:latlong2/latlong.dart';
 
@@ -25,6 +27,9 @@ class _PolylinePerfStressPageState extends State<PolylinePerfStressPage> {
   @override
   void initState() {
     super.initState();
+
+    showNoWebPerfOverlaySnackbar(context);
+
     final random = Random(1234);
     for (int i = 1; i < 300000; i++) {
       final lat = (random.nextDouble() - 0.5) * 0.001;
@@ -81,12 +86,13 @@ class _PolylinePerfStressPageState extends State<PolylinePerfStressPage> {
                   setState(() => simplificationTolerance = v),
             ),
           ),
-          Positioned(
-            bottom: 16,
-            left: 0,
-            right: 0,
-            child: PerformanceOverlay.allEnabled(),
-          ),
+          if (!kIsWeb)
+            Positioned(
+              bottom: 16,
+              left: 0,
+              right: 0,
+              child: PerformanceOverlay.allEnabled(),
+            ),
         ],
       ),
     );

example/lib/widgets/show_no_web_perf_overlay_snackbar.dart

@@ -0,0 +1,14 @@
+import 'package:flutter/foundation.dart';
+import 'package:flutter/material.dart';
+
+void showNoWebPerfOverlaySnackbar(BuildContext context) {
+  if (kIsWeb) {
+    WidgetsBinding.instance.addPostFrameCallback(
+      (_) => ScaffoldMessenger.of(context).showSnackBar(
+        const SnackBar(
+          content: Text('Cannot show performance graph overlay on web'),
+        ),
+      ),
+    );
+  }
+}