Support abstract getters without parameters.

dart/lib/compiler/implementation/tree/nodes.dart

Index: dart/lib/compiler/implementation/tree/nodes.dart
diff --git a/dart/lib/compiler/implementation/tree/nodes.dart b/dart/lib/compiler/implementation/tree/nodes.dart
index ba05232ec1449caa83f933401b39cbcd3d7289d4..4c03d1f08e03c90782439e8366110339de8b0320 100644
--- a/dart/lib/compiler/implementation/tree/nodes.dart
+++ b/dart/lib/compiler/implementation/tree/nodes.dart
@@ -646,7 +646,7 @@ class Literal<T> extends Expression {
 
   Literal(Token this.token, DecodeErrorHandler this.handler);
 
-  abstract T get value();
+  abstract T get value;
 
   visitChildren(Visitor visitor) {}
 
@@ -780,8 +780,8 @@ class StringQuoting {
   * Superclass for classes representing string literals.
   */
 class StringNode extends Expression {
-  abstract DartString get dartString();
-  abstract bool get isInterpolation();
+  abstract DartString get dartString;
+  abstract bool get isInterpolation;
 
   StringNode asStringNode() => this;
 }
@@ -1009,7 +1009,7 @@ class VariableDefinitions extends Statement {
 }
 
 class Loop extends Statement {
-  abstract Expression get condition();
+  abstract Expression get condition;
   final Statement body;
 
   Loop(this.body);