Added test case.

Author: DanielRosenwasser

tests/cases/compiler/declarationEmitForDefaultExportClassExtendingExpression01.ts

@@ -0,0 +1,21 @@
+// @declaration: true
+
+interface Greeter {
+    getGreeting(): string;
+}
+
+interface GreeterConstructor {
+    new (): Greeter;
+}
+
+class A {
+    getGreeting() {
+        return 'hello';
+    }
+}
+
+const getGreeterBase = (): GreeterConstructor => A;
+
+export default class extends getGreeterBase() {
+}
+