Output module-local enum in legacy module.

Related to #872.

Tested:
  unit tests

Author: nbeloglazov

src/main/java/com/google/javascript/clutz/DeclarationGenerator.java

@@ -1893,6 +1893,7 @@ private void visitEnumType(String symbolName, String qualifiedName, EnumType typ
         emit(elementsTypeName);
         emit(";");
         emitBreak();
+        typesUsed.add(elementsTypeName);
         return;
       }
 

src/test/java/com/google/javascript/clutz/testdata/partial/declare_legacy_namespace_enu.d.ts

@@ -0,0 +1,19 @@
+// Generated from src/test/java/com/google/javascript/clutz/testdata/partial/declare_legacy_namespace_enu.js
+declare namespace ಠ_ಠ.clutz.declare.legacy.namespace.enu {
+  export import E = module$contents$declare$legacy$namespace$enu_E ;
+}
+declare module 'goog:declare.legacy.namespace.enu' {
+  import enu = ಠ_ಠ.clutz.declare.legacy.namespace.enu;
+  export = enu;
+}
+// Generated from src/test/java/com/google/javascript/clutz/testdata/partial/declare_legacy_namespace_enu.js
+declare namespace ಠ_ಠ.clutz {
+  enum module$contents$declare$legacy$namespace$enu_E {
+    A = 1.0 ,
+    B = 2.0 ,
+    C = 3.0 ,
+  }
+}
+declare namespace ಠ_ಠ.clutz.module$exports$declare$legacy$namespace$enu {
+  export import E = ಠ_ಠ.clutz.module$contents$declare$legacy$namespace$enu_E ;
+}

src/test/java/com/google/javascript/clutz/testdata/partial/declare_legacy_namespace_enu.js

@@ -0,0 +1,17 @@
+// This test is the same as declare_legacy_namespace_enum.js with the
+// difference that it doesn't use "enum" which is reserved keyword and triggers
+// separate flow in Clutz.
+
+goog.module('declare.legacy.namespace.enu');
+goog.module.declareLegacyNamespace();
+
+/**
+ * @enum {number}
+ */
+const E = {
+  A: 1,
+  B: 2,
+  C: 3
+};
+
+exports.E = E;

src/test/java/com/google/javascript/clutz/testdata/partial/declare_legacy_namespace_enum.d.ts

@@ -0,0 +1,18 @@
+declare namespace ಠ_ಠ.clutz.declare.legacy {
+  let namespace : { enum : { E : module$contents$declare$legacy$namespace$enum_E } };
+}
+declare module 'goog:declare.legacy.namespace.enum' {
+  import enum_ = ಠ_ಠ.clutz.declare.legacy.namespace;
+  export default enum_.enum;
+}
+// Generated from src/test/java/com/google/javascript/clutz/testdata/partial/declare_legacy_namespace_enum.js
+declare namespace ಠ_ಠ.clutz {
+  enum module$contents$declare$legacy$namespace$enum_E {
+    A = 1.0 ,
+    B = 2.0 ,
+    C = 3.0 ,
+  }
+}
+declare namespace ಠ_ಠ.clutz.module$exports$declare$legacy$namespace$enum {
+  export import E = ಠ_ಠ.clutz.module$contents$declare$legacy$namespace$enum_E ;
+}

src/test/java/com/google/javascript/clutz/testdata/partial/declare_legacy_namespace_enum.js

@@ -0,0 +1,13 @@
+goog.module('declare.legacy.namespace.enum');
+goog.module.declareLegacyNamespace();
+
+/**
+ * @enum {number}
+ */
+const E = {
+  A: 1,
+  B: 2,
+  C: 3
+};
+
+exports.E = E;