Support top-level field declaration and assignment in analyzer2dart.

pkg/compiler/lib/src/dart_backend/backend_ast_emitter.dart

Index: pkg/compiler/lib/src/dart_backend/backend_ast_emitter.dart
diff --git a/pkg/compiler/lib/src/dart_backend/backend_ast_emitter.dart b/pkg/compiler/lib/src/dart_backend/backend_ast_emitter.dart
index 8a86eda794f38ae280b234949db7f41412ce990d..1539ba8b4f8cbd02169ca321156a86fafe28e74f 100644
--- a/pkg/compiler/lib/src/dart_backend/backend_ast_emitter.dart
+++ b/pkg/compiler/lib/src/dart_backend/backend_ast_emitter.dart
@@ -80,22 +80,26 @@ class ASTEmitter extends tree.Visitor<dynamic, Expression> {
 
   FieldDefinition emitField(tree.FieldDefinition definition) {
     currentElement = definition.element;
-    visitStatement(definition.body);
-    List<Statement> bodyParts;
-    for (tree.Variable variable in variableNames.keys) {
-      if (!declaredVariables.contains(variable)) {
-        addDeclaration(variable);
+    Expression initializer;
+    if (definition.hasInitializer) {
+      visitStatement(definition.body);
+      List<Statement> bodyParts;
+      for (tree.Variable variable in variableNames.keys) {
+        if (!declaredVariables.contains(variable)) {
+          addDeclaration(variable);
+        }
       }
-    }
-    if (variables.length > 0) {
-      bodyParts = new List<Statement>();
-      bodyParts.add(new VariableDeclarations(variables));
-      bodyParts.addAll(statementBuffer);
-    } else {
-      bodyParts = statementBuffer;
+      if (variables.length > 0) {
+        bodyParts = new List<Statement>();
+        bodyParts.add(new VariableDeclarations(variables));
+        bodyParts.addAll(statementBuffer);
+      } else {
+        bodyParts = statementBuffer;
+      }
+      initializer = ensureExpression(bodyParts);
     }
 
-    return new FieldDefinition(definition.element, ensureExpression(bodyParts));
+    return new FieldDefinition(definition.element, initializer);
   }
 
   /// Returns an expression that will evaluate all of [bodyParts].