Increased WriteBuffers starting capacity to 64 bytes. (#101790)

Author: gaaclarke

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

@@ -13,10 +13,14 @@ import 'dart:typed_data';
 /// The byte order used is [Endian.host] throughout.
 class WriteBuffer {
   /// Creates an interface for incrementally building a [ByteData] instance.
-  factory WriteBuffer() {
+  /// [startCapacity] determines the start size of the [WriteBuffer] in bytes.
+  /// The closer that value is to the real size used, the better the
+  /// performance.
+  factory WriteBuffer({int startCapacity = 8}) {
+    assert(startCapacity > 0);
     final ByteData eightBytes = ByteData(8);
     final Uint8List eightBytesAsList = eightBytes.buffer.asUint8List();
-    return WriteBuffer._(Uint8List(8), eightBytes, eightBytesAsList);
+    return WriteBuffer._(Uint8List(startCapacity), eightBytes, eightBytesAsList);
   }
 
   WriteBuffer._(this._buffer, this._eightBytes, this._eightBytesAsList);

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

@@ -310,7 +310,7 @@ class StandardMessageCodec implements MessageCodec<Object?> {
   ByteData? encodeMessage(Object? message) {
     if (message == null)
       return null;
-    final WriteBuffer buffer = WriteBuffer();
+    final WriteBuffer buffer = WriteBuffer(startCapacity: 64);
     writeValue(buffer, message);
     return buffer.done();
   }

packages/flutter/test/foundation/serialization_test.dart

@@ -124,5 +124,11 @@ void main() {
       write.done();
       expect(() => write.done(), throwsStateError);
     });
+    test('empty WriteBuffer', () {
+      expect(() => WriteBuffer(startCapacity: 0), throwsAssertionError);
+    });
+    test('size 1', () {
+      expect(() => WriteBuffer(startCapacity: 1), returnsNormally);
+    });
   });
 }