Fix memory leaks in WidgetInspector and WidgetInspectorService. (#135828)

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

@@ -372,6 +372,12 @@ class _ScreenshotData {
   set screenshotOffset(Offset offset) {
     containerLayer.offset = offset;
   }
+
+  /// Releases allocated resources.
+  @mustCallSuper
+  void dispose() {
+    containerLayer.dispose();
+  }
 }
 
 /// A place to paint to build screenshots of [RenderObject]s.
@@ -550,7 +556,7 @@ class _ScreenshotPaintingContext extends PaintingContext {
     Rect renderBounds, {
     double pixelRatio = 1.0,
     bool debugPaint = false,
-  }) {
+  }) async {
     RenderObject repaintBoundary = renderObject;
     while (!repaintBoundary.isRepaintBoundary) {
       repaintBoundary = repaintBoundary.parent!;
@@ -604,7 +610,15 @@ class _ScreenshotPaintingContext extends PaintingContext {
     // been called successfully for all layers in the regular scene.
     repaintBoundary.debugLayer!.buildScene(ui.SceneBuilder());
 
-    return data.containerLayer.toImage(renderBounds, pixelRatio: pixelRatio);
+    final ui.Image image;
+
+    try {
+      image = await data.containerLayer.toImage(renderBounds, pixelRatio: pixelRatio);
+    } finally {
+      data.dispose();
+    }
+
+    return image;
   }
 }
 
@@ -1285,6 +1299,7 @@ mixin WidgetInspectorService {
           return <String, Object?>{'result': null};
         }
         final ByteData? byteData = await image.toByteData(format:ui.ImageByteFormat.png);
+        image.dispose();
 
         return <String, Object>{
           'result': base64.encoder.convert(Uint8List.view(byteData!.buffer)),
@@ -3141,7 +3156,7 @@ class _InspectorOverlayLayer extends Layer {
   _InspectorOverlayRenderState? _lastState;
 
   /// Picture generated from _lastState.
-  late ui.Picture _picture;
+  ui.Picture? _picture;
 
   TextPainter? _textPainter;
   double? _textPainterMaxWidth;
@@ -3150,6 +3165,7 @@ class _InspectorOverlayLayer extends Layer {
   void dispose() {
     _textPainter?.dispose();
     _textPainter = null;
+    _picture?.dispose();
     super.dispose();
   }
 
@@ -3184,9 +3200,10 @@ class _InspectorOverlayLayer extends Layer {
 
     if (state != _lastState) {
       _lastState = state;
+      _picture?.dispose();
       _picture = _buildPicture(state);
     }
-    builder.addPicture(Offset.zero, _picture);
+    builder.addPicture(Offset.zero, _picture!);
   }
 
   ui.Picture _buildPicture(_InspectorOverlayRenderState state) {