Support abstract getters without parameters.

dart/lib/compiler/implementation/ssa/nodes.dart

Index: dart/lib/compiler/implementation/ssa/nodes.dart
diff --git a/dart/lib/compiler/implementation/ssa/nodes.dart b/dart/lib/compiler/implementation/ssa/nodes.dart
index 03e81941aeea80906fb087bb37320ed61e26d52d..2080a6e6fbf36474fbae29697a018a5c05a1dcfb 100644
--- a/dart/lib/compiler/implementation/ssa/nodes.dart
+++ b/dart/lib/compiler/implementation/ssa/nodes.dart
@@ -1528,7 +1528,7 @@ class HInvokeBinary extends HInvokeStatic {
   HInstruction get left => inputs[1];
   HInstruction get right => inputs[2];
 
-  abstract BinaryOperation get operation();
+  abstract BinaryOperation get operation;
   abstract isBuiltin(HTypeMap types);
 }
 
@@ -1589,7 +1589,7 @@ class HBinaryArithmetic extends HInvokeBinary {
   }
 
   // TODO(1603): The class should be marked as abstract.
-  abstract BinaryOperation get operation();
+  abstract BinaryOperation get operation;
 }
 
 class HAdd extends HBinaryArithmetic {
@@ -1836,7 +1836,7 @@ class HInvokeUnary extends HInvokeStatic {
 
   HType computeLikelyType(HTypeMap types) => HType.NUMBER;
 
-  abstract UnaryOperation get operation();
+  abstract UnaryOperation get operation;
 }
 
 class HNegate extends HInvokeUnary {
@@ -2170,7 +2170,7 @@ class HRelational extends HInvokeBinary {
   bool isBuiltin(HTypeMap types)
       => left.isNumber(types) && right.isNumber(types);
   // TODO(1603): the class should be marked as abstract.
-  abstract BinaryOperation get operation();
+  abstract BinaryOperation get operation;
 }
 
 class HEquals extends HRelational {