Replaced FlexDirection with Axis. (#5896)

Fixes #4618.

examples/layers/rendering/flex_layout.dart

@@ -10,7 +10,7 @@ import 'package:flutter/rendering.dart';
 import 'src/solid_color_box.dart';
 
 void main() {
-  RenderFlex table = new RenderFlex(direction: FlexDirection.vertical);
+  RenderFlex table = new RenderFlex(direction: Axis.vertical);
 
   void addAlignmentRow(CrossAxisAlignment crossAxisAlignment) {
     TextStyle style = const TextStyle(color: const Color(0xFF000000));
@@ -50,7 +50,7 @@ void main() {
     const TextStyle style = const TextStyle(color: const Color(0xFF000000));
     RenderParagraph paragraph = new RenderParagraph(new TextSpan(style: style, text: '$justify'));
     table.add(new RenderPadding(child: paragraph, padding: new EdgeInsets.only(top: 20.0)));
-    RenderFlex row = new RenderFlex(direction: FlexDirection.horizontal);
+    RenderFlex row = new RenderFlex(direction: Axis.horizontal);
     row.add(new RenderSolidColorBox(const Color(0xFFFFCCCC), desiredSize: new Size(80.0, 60.0)));
     row.add(new RenderSolidColorBox(const Color(0xFFCCFFCC), desiredSize: new Size(64.0, 60.0)));
     row.add(new RenderSolidColorBox(const Color(0xFFCCCCFF), desiredSize: new Size(160.0, 60.0)));

examples/layers/widgets/spinning_mixed.dart

@@ -93,7 +93,7 @@ void main() {
   RenderProxyBox proxy = new RenderProxyBox();
   attachWidgetTreeToRenderTree(proxy);
 
-  RenderFlex flexRoot = new RenderFlex(direction: FlexDirection.vertical);
+  RenderFlex flexRoot = new RenderFlex(direction: Axis.vertical);
   addFlexChildSolidColor(flexRoot, const Color(0xFFFF00FF), flex: 1);
   flexRoot.add(proxy);
   addFlexChildSolidColor(flexRoot, const Color(0xFF0000FF), flex: 1);

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

@@ -20,7 +20,7 @@ export 'package:flutter/rendering.dart' show
     CustomClipper,
     CustomPainter,
     FixedColumnCountGridDelegate,
-    FlexDirection,
+    Axis,
     FlowDelegate,
     FlowPaintingContext,
     FractionalOffsetTween,
@@ -1823,7 +1823,7 @@ class Flex extends MultiChildRenderObjectWidget {
   /// [CrossAxisAlignment.baseline], then [textBaseline] must not be null.
   Flex({
     Key key,
-    this.direction: FlexDirection.horizontal,
+    this.direction: Axis.horizontal,
     this.mainAxisAlignment: MainAxisAlignment.start,
     this.mainAxisSize: MainAxisSize.max,
     this.crossAxisAlignment: CrossAxisAlignment.center,
@@ -1838,7 +1838,7 @@ class Flex extends MultiChildRenderObjectWidget {
   }
 
   /// The direction to use as the main axis.
-  final FlexDirection direction;
+  final Axis direction;
 
   /// How the children should be placed along the main axis.
   final MainAxisAlignment mainAxisAlignment;
@@ -1902,7 +1902,7 @@ class Row extends Flex {
   }) : super(
     children: children,
     key: key,
-    direction: FlexDirection.horizontal,
+    direction: Axis.horizontal,
     mainAxisAlignment: mainAxisAlignment,
     mainAxisSize: mainAxisSize,
     crossAxisAlignment: crossAxisAlignment,
@@ -1930,7 +1930,7 @@ class Column extends Flex {
   }) : super(
     children: children,
     key: key,
-    direction: FlexDirection.vertical,
+    direction: Axis.vertical,
     mainAxisAlignment: mainAxisAlignment,
     mainAxisSize: mainAxisSize,
     crossAxisAlignment: crossAxisAlignment,

packages/flutter/test/rendering/box_test.dart

@@ -39,7 +39,7 @@ void main() {
     );
     RenderBox flex = new RenderFlex(
       children: <RenderBox>[padding],
-      direction: FlexDirection.vertical,
+      direction: Axis.vertical,
       crossAxisAlignment: CrossAxisAlignment.stretch
     );
     RenderBox outer = new RenderDecoratedBox(

packages/flutter/test/rendering/flex_test.dart

@@ -24,7 +24,7 @@ void main() {
       additionalConstraints: const BoxConstraints.expand()
     );
     RenderFlex flex = new RenderFlex(
-      direction: FlexDirection.vertical,
+      direction: Axis.vertical,
       children: <RenderBox>[
         new RenderConstrainedBox(additionalConstraints: new BoxConstraints.tightFor(height: 200.0)),
         flexible,
@@ -46,7 +46,7 @@ void main() {
       additionalConstraints: const BoxConstraints.expand()
     );
     RenderFlex flex = new RenderFlex(
-      direction: FlexDirection.horizontal,
+      direction: Axis.horizontal,
       children: <RenderBox>[
         new RenderConstrainedBox(additionalConstraints: new BoxConstraints.tightFor(width: 200.0)),
         flexible,
@@ -65,7 +65,7 @@ void main() {
 
   test('Vertical Flipped Constraints', () {
     RenderFlex flex = new RenderFlex(
-      direction: FlexDirection.vertical,
+      direction: Axis.vertical,
       children: <RenderBox>[
         new RenderAspectRatio(aspectRatio: 1.0),
       ]
@@ -81,7 +81,7 @@ void main() {
   test('Defaults', () {
     RenderFlex flex = new RenderFlex();
     expect(flex.crossAxisAlignment, equals(CrossAxisAlignment.center));
-    expect(flex.direction, equals(FlexDirection.horizontal));
+    expect(flex.direction, equals(Axis.horizontal));
   });
 
   test('Parent data', () {
@@ -129,7 +129,7 @@ void main() {
     expect(box2.size.width, equals(100.0));
     expect(box2.size.height, equals(100.0));
 
-    flex.direction = FlexDirection.vertical;
+    flex.direction = Axis.vertical;
     pumpFrame();
     expect(box1.size.width, equals(100.0));
     expect(box1.size.height, equals(0.0));
@@ -157,7 +157,7 @@ void main() {
     expect(getOffset(box3).dx, equals(350.0));
     expect(box3.size.width, equals(100.0));
 
-    flex.direction = FlexDirection.vertical;
+    flex.direction = Axis.vertical;
     pumpFrame();
     expect(getOffset(box1).dy, equals(25.0));
     expect(box1.size.height, equals(100.0));