Redo "Dummy receiver optimization"

sdk/lib/_internal/compiler/implementation/constants.dart

Index: sdk/lib/_internal/compiler/implementation/constants.dart
diff --git a/sdk/lib/_internal/compiler/implementation/constants.dart b/sdk/lib/_internal/compiler/implementation/constants.dart
index d0305244a8c765a205ba3b97d9606a9da83f2350..272fd6a5cd201f82c7fd1eec4ceaa17e7bb834a8 100644
--- a/sdk/lib/_internal/compiler/implementation/constants.dart
+++ b/sdk/lib/_internal/compiler/implementation/constants.dart
@@ -17,6 +17,7 @@ abstract class ConstantVisitor<R> {
   R visitConstructed(ConstructedConstant constant);
   R visitType(TypeConstant constant);
   R visitInterceptor(InterceptorConstant constant);
+  R visitDummyReceiver(DummyReceiverConstant constant);
 }
 
 abstract class Constant {
@@ -41,6 +42,7 @@ abstract class Constant {
   bool isType() => false;
   bool isSentinel() => false;
   bool isInterceptor() => false;
+  bool isDummyReceiver() => false;
 
   bool isNaN() => false;
   bool isMinusZero() => false;
@@ -538,6 +540,33 @@ class InterceptorConstant extends Constant {
   }
 }
 
+class DummyReceiverConstant extends Constant {
+  final ti.TypeMask typeMask;
+
+  DummyReceiverConstant(this.typeMask);
+
+  bool isDummyReceiver() => true;
+
+  bool operator ==(other) {
+    return other is DummyReceiverConstant
+        && typeMask == other.typeMask;
+  }
+
+  get hashCode => typeMask.hashCode;
+
+  List<Constant> getDependencies() => const <Constant>[];
+
+  accept(ConstantVisitor visitor) => visitor.visitDummyReceiver(this);
+
+  DartType computeType(Compiler compiler) => compiler.types.dynamicType;
+
+  ti.TypeMask computeMask(Compiler compiler) => typeMask;
+
+  String toString() {
+    return 'DummyReceiverConstant($typeMask)';
+  }
+}
+
 class ConstructedConstant extends ObjectConstant {
   final List<Constant> fields;
   final int hashCode;