Pass shadowColor param to SceneBuilder (#15714)

* pass shadowColor param to SceneBuilder

* add doc comment and diagnostic node for shadowColor

* Add missing shadowColor param

packages/flutter/lib/src/rendering/layer.dart

@@ -764,9 +764,11 @@ class PhysicalModelLayer extends ContainerLayer {
     @required this.clipPath,
     @required this.elevation,
     @required this.color,
+    @required this.shadowColor,
   }) : assert(clipPath != null),
        assert(elevation != null),
-       assert(color != null);
+       assert(color != null),
+       assert(shadowColor != null);
 
   /// The path to clip in the parent's coordinate system.
   ///
@@ -786,6 +788,9 @@ class PhysicalModelLayer extends ContainerLayer {
   /// (as described at [Layer]).
   Color color;
 
+  /// The shadow color.
+  Color shadowColor;
+
   @override
   void addToScene(ui.SceneBuilder builder, Offset layerOffset) {
     if (!debugDisablePhysicalShapeLayers)
@@ -793,6 +798,7 @@ class PhysicalModelLayer extends ContainerLayer {
         path: clipPath.shift(layerOffset),
         elevation: elevation,
         color: color,
+        shadowColor: shadowColor,
       );
     addChildrenToScene(builder, layerOffset);
     if (!debugDisablePhysicalShapeLayers)

packages/flutter/lib/src/rendering/proxy_box.dart

@@ -1495,6 +1495,7 @@ abstract class _RenderPhysicalModelBase<T> extends _RenderCustomClip<T> {
     super.debugFillProperties(description);
     description.add(new DoubleProperty('elevation', elevation));
     description.add(new DiagnosticsProperty<Color>('color', color));
+    description.add(new DiagnosticsProperty<Color>('shadowColor', color));
   }
 }
 
@@ -1596,6 +1597,7 @@ class RenderPhysicalModel extends _RenderPhysicalModelBase<RRect> {
           clipPath: offsetClipPath,
           elevation: elevation,
           color: color,
+          shadowColor: shadowColor,
         );
         context.pushLayer(physicalModel, super.paint, offset, childPaintBounds: offsetBounds);
       } else {
@@ -1702,6 +1704,7 @@ class RenderPhysicalShape extends _RenderPhysicalModelBase<Path> {
           clipPath: offsetPath,
           elevation: elevation,
           color: color,
+          shadowColor: shadowColor,
         );
         context.pushLayer(physicalModel, super.paint, offset, childPaintBounds: offsetBounds);
       } else {