Enable setting the UINode key for ParentDataNodes

sky/sdk/lib/framework/fn2.dart

Index: sky/sdk/lib/framework/fn2.dart
diff --git a/sky/sdk/lib/framework/fn2.dart b/sky/sdk/lib/framework/fn2.dart
index 9ca123fcf61108d89ec67221dad9ca66b7e1672d..98e53219622051823907209dcf0ad904ee801097 100644
--- a/sky/sdk/lib/framework/fn2.dart
+++ b/sky/sdk/lib/framework/fn2.dart
@@ -154,7 +154,7 @@ abstract class UINode {
 abstract class ContentNode extends UINode {
   UINode content;
 
-  ContentNode(UINode content) : this.content = content, super(key: content._key);
+  ContentNode(UINode content, {Object key}) : this.content = content, super(key: key);

[abarth-chromium, 2015/06/09 17:37:01]

We've been putting a space inside the { } so { Object key }

Not sure if that's real dart style or we just made it up.

[hansmuller, 2015/06/09 17:48:03]

Done.

I've been taking advantage of the fact that Sky style doesn't appear to be too
strict about lines that are wider than 80 chars. I hope that's OK.

 
   void _sync(UINode old, dynamic slot) {
     UINode oldContent = old == null ? null : (old as ContentNode).content;
@@ -173,7 +173,7 @@ abstract class ContentNode extends UINode {
 class ParentDataNode extends ContentNode {
   final ParentData parentData;
 
-  ParentDataNode(UINode content, this.parentData): super(content);
+  ParentDataNode(UINode content, this.parentData, {Object key}): super(content, key: key);
 }
 
 typedef void GestureEventListener(sky.GestureEvent e);
@@ -754,8 +754,8 @@ class FlexContainer extends MultiChildRenderObjectWrapper {
 }
 
 class FlexExpandingChild extends ParentDataNode {
-  FlexExpandingChild(UINode content, [int flex = 1])
-    : super(content, new FlexBoxParentData()..flex = flex);
+  FlexExpandingChild(UINode content, {int flex: 1, Object key})

[Hixie, 2015/06/09 17:40:08]

I think I'd make the flex be an optional positional argument, and the key an
optional named argument. Having to explicitly give the 'flex' name everywhere is
redundant with the class name.

+    : super(content, new FlexBoxParentData()..flex = flex, key: key);
 }
 
 class Image extends RenderObjectWrapper {