implement opassign, fix bugs in pre/postfix, introduce a let* helper

lib/src/info.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 /// Defines static information collected by the type checker and used later by
 /// emitters to generate code.
 library dev_compiler.src.info;
 
 import 'dart:mirrors';
 
@@ skipping 147 matching lines @@
 
   AstNode get node => expression;
   DartType _convertedType;
 
   Conversion(this.rules, this.expression) {
     this._convertedType = _getConvertedType();
   }
 
   DartType get baseType => rules.getStaticType(expression);
   DartType get convertedType => _convertedType;
+  DartType get staticType => _convertedType;
 
   DartType _getConvertedType();
 
   // safe iff this cannot throw
   bool get safe => false;
 
   Level get level => safe ? Level.CONFIG : Level.INFO;
 
   String get description => '${this.runtimeType}: $baseType to $convertedType';
 
@@ skipping 544 matching lines @@
   for (var cls in declarations.where((d) => d is ClassMirror)) {
     if (cls.isSubtypeOf(infoMirror)) {
       allTypes.add(cls);
       baseTypes.add(cls.superclass);
     }
   }
   allTypes.removeAll(baseTypes);
   return new List<Type>.from(allTypes.map((mirror) => mirror.reflectedType))
     ..sort((t1, t2) => '$t1'.compareTo('$t2'));
 }();