Remove _emptyList from fn2.dart

We can use const [] instead and we'll be sure we don't mutate this constant.

R=ianh@google.com

Review URL: https://codereview.chromium.org/1178623002.

sdk/lib/framework/fn2.dart

@@ -530,8 +530,6 @@ class CustomPaint extends OneChildRenderObjectWrapper {
 
 }
 
-final List<UINode> _emptyList = new List<UINode>();
-
 abstract class MultiChildRenderObjectWrapper extends RenderObjectWrapper {
 
   // In MultiChildRenderObjectWrapper subclasses, slots are RenderObject nodes
@@ -540,10 +538,8 @@ abstract class MultiChildRenderObjectWrapper extends RenderObjectWrapper {
   MultiChildRenderObjectWrapper({
     Object key,
     List<UINode> children
-  }) : this.children = children == null ? _emptyList : children,
-  super(
-    key: key
-  ) {
+  }) : this.children = children == null ? const [] : children,
+       super(key: key) {
     assert(!_debugHasDuplicateIds());
   }
 

specs/style-guide.md

@@ -51,8 +51,7 @@ same order (unless the order matters).
 
 All variables and arguments are typed; don't use "var", "dynamic", or
 "Object" in any case where you could figure out the actual type.
-Always specialise generic types where possible. Even for ```[]``` and
-```{}``` literals, include the types.
+Always specialise generic types where possible.
 
 Aim for a line length of 80 characters, but go over if breaking the
 line would make it less readable.