Specs: fix typos in style2.md, checkin forgotten builtins.md, add guard feature to runloop.md, rena…

sky/specs/style2.md

 Sky Style Language
 ==================
 
-Note: This is a work in progress that will eventually replace
-(style.md)[style.md].
+This is a trimmed down version of the API in (style.md)[style.md]
+that is intended to be a stepping stone to the long-term world where
+there are no hard-coded properties in the engine.
 
 The Sky style API looks like the following:
 
 ```dart
 
   // all properties can be set as strings:
   element.style['color'] = 'blue';
 
   // some properties have dedicated APIs
   // color
@@ skipping 34 matching lines @@
   // you can clone a StyleDeclaration object:
   var style2 = new StyleDeclaration.clone(style);
 ```
 
 The dart:sky library contains the following to define this API:
 
 ```dart
 import 'dart:mirrors';
 import 'dart:math';
 
-class WeakMap<Key, Value> {
-  // This is not actually a weak map right now, because Dart doesn't let us have weak references.
-  // We should fix that, or else we're going to keep alive every object you ever tear off through
-  // the StyleDeclaration API, even if you never use it again, until the StyleDeclaration object
-  // itself is GC'ed, which is likely when the element is GC'ed, which is likely never.
-  Map<Key, Value> _map = new Map<Key, Value>();
-  operator[](Key key) => _map[key];
-  operator[]=(Key key, Value value) => _map[key] = value;
-  bool containsKey(Key key) => _map.containsKey(key);
-}
-
 typedef void StringSetter(Symbol propertySymbol, StyleDeclaration declaration, String value);
 typedef String StringGetter(Symbol propertySymbol, StyleDeclaration declaration);
 typedef Property ObjectConstructor(Symbol propertySymbol, StyleDeclaration declaration);
 
 class PropertyTable {
   const PropertyTable({this.symbol, this.inherited, this.stringGetter, this.stringSetter, this.objectConstructor});
   final Symbol symbol;
   final bool inherited;
   final StringSetter stringSetter;
   final StringGetter stringGetter;
@@ skipping 31 matching lines @@
   }
 
   operator []=(String propertyName, String newValue) {
     var propertySymbol = new Symbol(propertyName);
     if (_registeredProperties.containsKey(propertySymbol))
       return _registeredProperties[propertySymbol].stringSetter(propertySymbol, this, newValue);
     throw new ArgumentError(propertyName);
   }
 
   // some properties expose dedicated APIs so you don't have to use string manipulation
-  WeakMap<Symbol, Property> _properties = new WeakMap<Symbol, Property>();
+  MapOfWeakReferences<Symbol, Property> _properties = new MapOfWeakReferences<Symbol, Property>();
   noSuchMethod(Invocation invocation) {
     Symbol propertySymbol;
     if (invocation.isSetter) {
       // when it's a setter, the name will be "foo=" rather than "foo"
       String propertyName = MirrorSystem.getName(invocation.memberName);
       assert(propertyName[propertyName.length-1] == '=');
       propertySymbol = new Symbol(propertyName.substring(0, propertyName.length-1));
     } else {
       propertySymbol = invocation.memberName;
     }
@@ skipping 38 matching lines @@
     throw new ArgumentError(value);
   }
 
   bool get inherit => _isInherit();
   void set inherit (value) {
     if (value == true)
       return _setInherit();
     throw new ArgumentError(value);
   }
 
-  void setter(dynamic value) {
-    if (value == initial)
-      return _setInitial();
-    if (value == inherit)
-      return _setInitial();
-    if (value == null)
-      return _unset();
-    throw new ArgumentError(value);
+  void setter(dynamic newValue) {
+    switch (newValue) {
+      case initial:
+        _setInitial();
+      case inherit:
+        _setInherit();
+      case null:
+        _unset();
+      default:
+        throw new ArgumentError(value);
+    }
   }
 
   external bool _isInitial();
   external void _setInitial();
   external bool _isInherit();
   external void _setInherit();
   external void _unset();
 }
 ```
 
@@ skipping 147 matching lines @@
   registerProperty(new PropertyTable(   
     symbol: #transform,
     inherited: false,
     stringSetter: transformPropertyStringSetter,
     stringGetter: transformPropertyStringGetter,
     objectConstructor: (Symbol propertySymbol, StyleDeclaration declaration) =>
                          new TransformProperty(propertySymbol, declaration)));
 }
 ```