Support enums in dart2js.

pkg/compiler/lib/src/ssa/builder.dart

 // Copyright (c) 2012, 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.
 
 part of ssa;
 
 /// A synthetic local variable only used with the SSA graph.
 ///
 /// For instance used for holding return value of function or the exception of a
 /// try-catch statement.
@@ skipping 1474 matching lines @@
     graph.entry.addBefore(graph.entry.last, parameter);
     HInstruction value =
         potentiallyCheckType(parameter, field.type);
     add(new HFieldSet(field, thisInstruction, value));
     return closeFunction();
   }
 
   HGraph buildLazyInitializer(VariableElement variable) {
     ast.Node node = variable.node;
     openFunction(variable, node);
-    assert(variable.initializer != null);
+    assert(invariant(variable, variable.initializer != null,
+        message: "Non-constant variable $variable has no initializer."));
     visit(variable.initializer);
     HInstruction value = pop();
     value = potentiallyCheckType(value, variable.type);
     closeAndGotoExit(new HReturn(value));
     return closeFunction();
   }
 
   /**
    * Returns the constructor body associated with the given constructor or
    * creates a new constructor body, if none can be found.
@@ skipping 5063 matching lines @@
     if (unaliased is TypedefType) throw 'unable to unalias $type';
     unaliased.accept(this, builder);
   }
 
   void visitDynamicType(DynamicType type, SsaBuilder builder) {
     JavaScriptBackend backend = builder.compiler.backend;
     ClassElement cls = backend.findHelper('DynamicRuntimeType');
     builder.push(new HDynamicType(type, new TypeMask.exact(cls, classWorld)));
   }
 }