Don't generate errors when failing to follow const constructor redirections.

editor/tools/plugins/com.google.dart.engine_test/src/com/google/dart/engine/resolver/CompileTimeErrorCodeTest.java

Index: editor/tools/plugins/com.google.dart.engine_test/src/com/google/dart/engine/resolver/CompileTimeErrorCodeTest.java
diff --git a/editor/tools/plugins/com.google.dart.engine_test/src/com/google/dart/engine/resolver/CompileTimeErrorCodeTest.java b/editor/tools/plugins/com.google.dart.engine_test/src/com/google/dart/engine/resolver/CompileTimeErrorCodeTest.java
index df9f062bab61a64cf624bb7fd3c53fd4706b9834..f001ed1a58d275a1456a0e7e466a2bf5164f691b 100644
--- a/editor/tools/plugins/com.google.dart.engine_test/src/com/google/dart/engine/resolver/CompileTimeErrorCodeTest.java
+++ b/editor/tools/plugins/com.google.dart.engine_test/src/com/google/dart/engine/resolver/CompileTimeErrorCodeTest.java
@@ -869,6 +869,19 @@ public class CompileTimeErrorCodeTest extends ResolverTestCase {
     verify(source);
   }
 
+  public void test_constEval_newInstance_externalFactoryConstConstructor() throws Exception {
+    // We can't evaluate "const A()" because its constructor is external.  But
+    // the code is correct--we shouldn't report an error.
+    Source source = addSource(createSource(//
+        "class A {",
+        "  external factory const A();",
+        "}",
+        "const x = const A();"));
+    resolve(source);
+    assertNoErrors(source);
+    verify(source);
+  }
+
   public void test_constEval_propertyExtraction_targetNotConst() throws Exception {
     Source source = addSource(createSource(//
         "class A {",