Support for alignItems (test incoming)

sky/sdk/lib/framework/rendering/flex.dart

Index: sky/sdk/lib/framework/rendering/flex.dart
diff --git a/sky/sdk/lib/framework/rendering/flex.dart b/sky/sdk/lib/framework/rendering/flex.dart
index 4def9d2d094b03771cf28998d2003b74052f7593..dc08cd73dc01882c1ed2a5ea42b92f1037d72251 100644
--- a/sky/sdk/lib/framework/rendering/flex.dart
+++ b/sky/sdk/lib/framework/rendering/flex.dart
@@ -19,6 +19,7 @@ class FlexBoxParentData extends BoxParentData with ContainerParentDataMixin<Rend
 }
 
 enum FlexDirection { horizontal, vertical }
+
 enum FlexJustifyContent {
   flexStart,
   flexEnd,
@@ -27,6 +28,12 @@ enum FlexJustifyContent {
   spaceAround,
 }
 
+enum FlexAlignItems {
+  flexStart,
+  flexEnd,
+  center,
+}
+
 typedef double _ChildSizingFunction(RenderBox child, BoxConstraints constraints);
 
 class RenderFlex extends RenderBox with ContainerRenderObjectMixin<RenderBox, FlexBoxParentData>,
@@ -35,8 +42,9 @@ class RenderFlex extends RenderBox with ContainerRenderObjectMixin<RenderBox, Fl
 
   RenderFlex({
     FlexDirection direction: FlexDirection.horizontal,
-    FlexJustifyContent justifyContent: FlexJustifyContent.flexStart
-  }) : _direction = direction, _justifyContent = justifyContent;
+    FlexJustifyContent justifyContent: FlexJustifyContent.flexStart,
+    FlexAlignItems alignItems: FlexAlignItems.center
+  }) : _direction = direction, _justifyContent = justifyContent, _alignItems = alignItems;
 
   FlexDirection _direction;
   FlexDirection get direction => _direction;
@@ -56,6 +64,15 @@ class RenderFlex extends RenderBox with ContainerRenderObjectMixin<RenderBox, Fl
     }
   }
 
+  FlexAlignItems _alignItems;
+  FlexAlignItems get alignItems => _alignItems;
+  void set alignItems (FlexAlignItems value) {
+    if (_alignItems != value) {
+      _alignItems = value;
+      markNeedsLayout();
+    }
+  }
+
   void setParentData(RenderBox child) {
     if (child.parentData is! FlexBoxParentData)
       child.parentData = new FlexBoxParentData();
@@ -334,7 +351,18 @@ class RenderFlex extends RenderBox with ContainerRenderObjectMixin<RenderBox, Fl
     double childMainPosition = leadingSpace;
     child = firstChild;
     while (child != null) {
-      double childCrossPosition = crossSize / 2.0 - _getCrossSize(child) / 2.0;
+      double childCrossPosition;
+      switch (_alignItems) {
+        case FlexAlignItems.flexStart:
+          childCrossPosition = 0.0;
+          break;
+        case FlexAlignItems.flexEnd:
+          childCrossPosition = crossSize - _getCrossSize(child);
+          break;
+        case FlexAlignItems.center:
+          childCrossPosition = crossSize / 2.0 - _getCrossSize(child) / 2.0;
+          break;
+      }
       switch (_direction) {
         case FlexDirection.horizontal:
           child.parentData.position = new Point(childMainPosition, childCrossPosition);