Fix #28740 demangle constructors in stack traces (A.A becomes new A).

tests/language/stacktrace_demangle_ctors_test.dart

+// Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+// Test that stack traces are properly demangled in constructors (#28740).
+
+import "package:expect/expect.dart";
+
+class SomeClass {
+  SomeClass.namedConstructor() {
+    throw new Exception();
+  }
+
+  SomeClass() {
+    throw new Exception();
+  }
+
+  factory SomeClass.useFactory() {
+    throw new Exception();
+  }
+}
+
+class OnlyHasFactory {
+  factory OnlyHasFactory() {
+    throw new Exception();
+  }
+}
+
+void main() {
+  try {
+    new SomeClass();
+  } on Exception catch (e, st) {
+    final stString = st.toString();
+    Expect.isTrue(stString.contains("new SomeClass"));
+    Expect.isFalse(stString.contains("SomeClass."));
+  }
+
+  try {
+    new SomeClass.namedConstructor();
+  } on Exception catch (e, st) {
+    final stString = st.toString();
+    Expect.isTrue(stString.contains("new SomeClass.namedConstructor"));
+  }
+
+  try {
+    new OnlyHasFactory();
+  } on Exception catch (e, st) {
+    final stString = st.toString();
+    Expect.isTrue(stString.contains("new OnlyHasFactory"));
+    Expect.isFalse(stString.contains("OnlyHasFactory."));
+  }
+
+  try {
+    new SomeClass.useFactory();
+  } on Exception catch (e, st) {
+    final stString = st.toString();
+    Expect.isTrue(stString.contains("new SomeClass.useFactory"));
+  }
+}