Made Card's margin configurable (#16203)

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

@@ -65,6 +65,7 @@ class Card extends StatelessWidget {
     this.color,
     this.elevation,
     this.shape,
+    this.margin: const EdgeInsets.all(4.0),
     this.child,
   }) : super(key: key);
 
@@ -91,6 +92,14 @@ class Card extends StatelessWidget {
   /// radius of 4.0.
   final ShapeBorder shape;
 
+  /// The empty space that surrounds the card.
+  ///
+  /// Defines the card's outer [Container.margin].
+  ///
+  /// The default margin is 4.0 logical pixels on all sides:
+  /// `EdgeInsets.all(4.0)`.
+  final EdgeInsetsGeometry margin;
+
   /// The widget below this widget in the tree.
   ///
   /// {@macro flutter.widgets.child}
@@ -101,7 +110,7 @@ class Card extends StatelessWidget {
     return new Semantics(
       container: true,
       child: new Container(
-        margin: const EdgeInsets.all(4.0),
+        margin: margin ?? const EdgeInsets.all(4.0),
         child: new Material(
           type: MaterialType.card,
           color: color ?? Theme.of(context).cardColor,

packages/flutter/test/material/card_test.dart

@@ -68,4 +68,51 @@ void main() {
     semantics.dispose();
   });
 
+  testWidgets('Card margin', (WidgetTester tester) async {
+    const Key contentsKey = const ValueKey<String>('contents');
+
+    await tester.pumpWidget(
+      new Container(
+        alignment: Alignment.topLeft,
+        child: new Card(
+          child: new Container(
+            key: contentsKey,
+            color: const Color(0xFF00FF00),
+            width: 100.0,
+            height: 100.0,
+          ),
+        ),
+      ),
+    );
+
+    // Default margin is 4
+    expect(tester.getTopLeft(find.byType(Card)), const Offset(0.0, 0.0));
+    expect(tester.getSize(find.byType(Card)), const Size(108.0, 108.0));
+
+    expect(tester.getTopLeft(find.byKey(contentsKey)), const Offset(4.0, 4.0));
+    expect(tester.getSize(find.byKey(contentsKey)), const Size(100.0, 100.0));
+
+    await tester.pumpWidget(
+      new Container(
+        alignment: Alignment.topLeft,
+        child: new Card(
+          margin: EdgeInsets.zero,
+          child: new Container(
+            key: contentsKey,
+            color: const Color(0xFF00FF00),
+            width: 100.0,
+            height: 100.0,
+          ),
+        ),
+      ),
+    );
+
+    // Specified margin is zero
+    expect(tester.getTopLeft(find.byType(Card)), const Offset(0.0, 0.0));
+    expect(tester.getSize(find.byType(Card)), const Size(100.0, 100.0));
+
+    expect(tester.getTopLeft(find.byKey(contentsKey)), const Offset(0.0, 0.0));
+    expect(tester.getSize(find.byKey(contentsKey)), const Size(100.0, 100.0));
+  });
+
 }