Various semantic checks regarding const and final.

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

Index: pkg/front_end/lib/src/fasta/kernel/kernel_procedure_builder.dart
diff --git a/pkg/front_end/lib/src/fasta/kernel/kernel_procedure_builder.dart b/pkg/front_end/lib/src/fasta/kernel/kernel_procedure_builder.dart
index 0893ca26e3d1c8867e1a52ba21880bb69577b9db..6a5b9a368b78ac1ecf135e7ebf9f92a8b0a0c22a 100644
--- a/pkg/front_end/lib/src/fasta/kernel/kernel_procedure_builder.dart
+++ b/pkg/front_end/lib/src/fasta/kernel/kernel_procedure_builder.dart
@@ -88,6 +88,10 @@ abstract class KernelFunctionBuilder
         return library.addCompileTimeError(
             newBody.fileOffset, "An external method can't have a body.");
       }
+      if (isConstructor && isConst) {
+        return library.addCompileTimeError(
+            newBody.fileOffset, "A const constructor can't have a body.");
+      }
     }
     actualBody = newBody;
     if (function != null) {