Don't allow invoking a constructor as 'const' if it wasn't declared 'const'.

compiler/java/com/google/dart/compiler/resolver/Resolver.java

Index: compiler/java/com/google/dart/compiler/resolver/Resolver.java
diff --git a/compiler/java/com/google/dart/compiler/resolver/Resolver.java b/compiler/java/com/google/dart/compiler/resolver/Resolver.java
index 4721b98aed25209a03404dbcf4996217f548951d..17ed6ccae8f5c430e7aedd83910cd73a4d853997 100644
--- a/compiler/java/com/google/dart/compiler/resolver/Resolver.java
+++ b/compiler/java/com/google/dart/compiler/resolver/Resolver.java
@@ -935,6 +935,12 @@ public class Resolver {
         constructor = checkIsConstructor(x, element);
       }
 
+      if (constructor != null) {
+        if (x.isConst() && !constructor.getModifiers().isConstant()) {
+          onError(x, ResolverErrorCode.CONST_AND_NONCONST_CONSTRUCTOR);
+        }
+      }
+
       return recordElement(x, constructor);
     }