Revert the new "physical model" shadow rendering code (#8636)

packages/flutter/lib/src/material/material.dart

@@ -7,6 +7,7 @@ import 'package:flutter/rendering.dart';
 import 'package:flutter/widgets.dart';
 
 import 'constants.dart';
+import 'shadows.dart';
 import 'theme.dart';
 
 /// Signature for the callback used by ink effects to obtain the rectangle for the effect.
@@ -228,28 +229,11 @@ class _MaterialState extends State<Material> with TickerProviderStateMixin {
       )
     );
     if (config.type == MaterialType.circle) {
-      contents = new PhysicalModel(
-        shape: BoxShape.circle,
-        elevation: config.elevation,
-        color: backgroundColor,
-        child: contents,
-      );
-    } else if (config.type == MaterialType.transparency) {
-      if (radius == null) {
-        contents = new ClipRect(child: contents);
-      } else {
-        contents = new ClipRRect(
-          borderRadius: radius,
-          child: contents
-        );
-      }
-    } else {
-      contents = new PhysicalModel(
-        shape: BoxShape.rectangle,
-        borderRadius: radius ?? BorderRadius.zero,
-        elevation: config.elevation,
-        color: backgroundColor,
-        child: contents,
+      contents = new ClipOval(child: contents);
+    } else if (kMaterialEdges[config.type] != null) {
+      contents = new ClipRRect(
+        borderRadius: radius,
+        child: contents
       );
     }
     if (config.type != MaterialType.transparency) {
@@ -263,6 +247,7 @@ class _MaterialState extends State<Material> with TickerProviderStateMixin {
         child: new Container(
           decoration: new BoxDecoration(
             borderRadius: radius,
+            boxShadow: config.elevation == 0 ? null : kElevationToShadow[config.elevation],
             backgroundColor: backgroundColor,
             shape: config.type == MaterialType.circle ? BoxShape.circle : BoxShape.rectangle
           ),