Create more synthetic kernel objects.

pkg/front_end/lib/src/fasta/kernel/body_builder.dart

Index: pkg/front_end/lib/src/fasta/kernel/body_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
index 283adcb7163dd835a9dd638aa8b8a32a58c0ea3d..dc87c7a5ff330ca818702f10d06f086b23b6baf9 100644
--- a/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/body_builder.dart
@@ -2279,10 +2279,10 @@ class BodyBuilder extends ScopeListener<JumpTarget> implements BuilderHelper {
         } else if (b.isConstructor) {
           initialTarget = b.target;
           if (type.isAbstract) {
-            push(evaluateArgumentsBefore(
+            push(new KernelSyntheticExpression(evaluateArgumentsBefore(
                 arguments,
                 buildAbstractClassInstantiationError(
-                    type.name, nameToken.charOffset)));
+                    type.name, nameToken.charOffset))));
             return;
           } else {
             target = initialTarget;
@@ -3053,9 +3053,8 @@ class BodyBuilder extends ScopeListener<JumpTarget> implements BuilderHelper {
     warning("The class '$className' is abstract and can't be instantiated.",
         charOffset);
     Builder constructor = library.loader.getAbstractClassInstantiationError();
-    return new KernelSyntheticExpression(new Throw(buildStaticInvocation(
-        constructor.target,
-        new KernelArguments(<Expression>[new StringLiteral(className)]))));
+    return new Throw(buildStaticInvocation(constructor.target,
+        new KernelArguments(<Expression>[new StringLiteral(className)])));
   }
 
   Statement buildCompileTimeErrorStatement(error, [int charOffset = -1]) {