Clear asset manager caches on memory pressure (#91353)

packages/flutter/lib/src/services/asset_bundle.dart

@@ -98,6 +98,9 @@ abstract class AssetBundle {
   /// loaded, the cache will be reread from the asset bundle.
   void evict(String key) { }
 
+  /// If this is a caching asset bundle, clear all cached data.
+  void clear() { }
+
   @override
   String toString() => '${describeIdentity(this)}()';
 }
@@ -215,6 +218,12 @@ abstract class CachingAssetBundle extends AssetBundle {
     _stringCache.remove(key);
     _structuredDataCache.remove(key);
   }
+
+  @override
+  void clear() {
+    _stringCache.clear();
+    _structuredDataCache.clear();
+  }
 }
 
 /// An [AssetBundle] that loads resources using platform messages.

packages/flutter/lib/src/services/binding.dart

@@ -113,7 +113,9 @@ mixin ServicesBinding on BindingBase, SchedulerBinding {
   /// [SystemChannels.system].
   @protected
   @mustCallSuper
-  void handleMemoryPressure() { }
+  void handleMemoryPressure() {
+    rootBundle.clear();
+  }
 
   /// Handler called for messages received on the [SystemChannels.system]
   /// message channel.

packages/flutter/test/services/binding_test.dart

@@ -51,8 +51,10 @@ class TestBinding extends BindingBase with SchedulerBinding, ServicesBinding {
 }
 
 void main() {
+  final TestBinding binding = TestBinding();
+
   test('Adds rootBundle LICENSES to LicenseRegistry', () async {
-    TestBinding().defaultBinaryMessenger.setMockMessageHandler('flutter/assets', (ByteData? message) async {
+    binding.defaultBinaryMessenger.setMockMessageHandler('flutter/assets', (ByteData? message) async {
       if (const StringCodec().decodeMessage(message) == 'NOTICES.Z' && !kIsWeb) {
         return Uint8List.fromList(gzip.encode(utf8.encode(combinedLicenses))).buffer.asByteData();
       }
@@ -76,4 +78,33 @@ void main() {
       equals(<String>['L2Paragraph1', 'L2Paragraph2', 'L2Paragraph3']),
     );
   });
+
+  test('didHaveMemoryPressure clears asset caches', () async {
+    int flutterAssetsCallCount = 0;
+    binding.defaultBinaryMessenger.setMockMessageHandler('flutter/assets', (ByteData? message) async {
+      flutterAssetsCallCount += 1;
+      return Uint8List.fromList('test_asset_data'.codeUnits).buffer.asByteData();
+    });
+
+    await rootBundle.loadString('test_asset');
+    expect(flutterAssetsCallCount, 1);
+    await rootBundle.loadString('test_asset2');
+    expect(flutterAssetsCallCount, 2);
+    await rootBundle.loadString('test_asset');
+    expect(flutterAssetsCallCount, 2);
+    await rootBundle.loadString('test_asset2');
+    expect(flutterAssetsCallCount, 2);
+
+    final ByteData message = const JSONMessageCodec().encodeMessage(<String, dynamic>{'type': 'memoryPressure'})!;
+    await ServicesBinding.instance!.defaultBinaryMessenger.handlePlatformMessage('flutter/system', message, (_) { });
+
+    await rootBundle.loadString('test_asset');
+    expect(flutterAssetsCallCount, 3);
+    await rootBundle.loadString('test_asset2');
+    expect(flutterAssetsCallCount, 4);
+    await rootBundle.loadString('test_asset');
+    expect(flutterAssetsCallCount, 4);
+    await rootBundle.loadString('test_asset2');
+    expect(flutterAssetsCallCount, 4);
+  });
 }