For c++, Generate enum classes instead of enum from mojom.

mojo/public/cpp/bindings/tests/union_unittest.cc

Index: mojo/public/cpp/bindings/tests/union_unittest.cc
diff --git a/mojo/public/cpp/bindings/tests/union_unittest.cc b/mojo/public/cpp/bindings/tests/union_unittest.cc
index e79ea9f76416a3daa814e8192e7d0647f6970536..261b0ee43b63b152a59bfab35b03ce5f801d142c 100644
--- a/mojo/public/cpp/bindings/tests/union_unittest.cc
+++ b/mojo/public/cpp/bindings/tests/union_unittest.cc
@@ -83,8 +83,8 @@ TEST(UnionTest, PlainOldDataGetterSetter) {
   EXPECT_TRUE(pod->is_f_bool());
   EXPECT_EQ(pod->which(), PodUnion::Tag::F_BOOL);
 
-  pod->set_f_enum(AN_ENUM_SECOND);
-  EXPECT_EQ(AN_ENUM_SECOND, pod->get_f_enum());
+  pod->set_f_enum(AnEnum::SECOND);
+  EXPECT_EQ(AnEnum::SECOND, pod->get_f_enum());
   EXPECT_TRUE(pod->is_f_enum());
   EXPECT_EQ(pod->which(), PodUnion::Tag::F_ENUM);
 }
@@ -135,7 +135,7 @@ TEST(UnionTest, PodSerialization) {
 
 TEST(UnionTest, EnumSerialization) {
   PodUnionPtr pod1(PodUnion::New());
-  pod1->set_f_enum(AN_ENUM_SECOND);
+  pod1->set_f_enum(AnEnum::SECOND);
 
   size_t size = GetSerializedSize_(pod1, false);
   EXPECT_EQ(16U, size);
@@ -147,7 +147,7 @@ TEST(UnionTest, EnumSerialization) {
   PodUnionPtr pod2 = PodUnion::New();
   Deserialize_(data, pod2.get());
 
-  EXPECT_EQ(AN_ENUM_SECOND, pod2->get_f_enum());
+  EXPECT_EQ(AnEnum::SECOND, pod2->get_f_enum());
   EXPECT_TRUE(pod2->is_f_enum());
   EXPECT_EQ(pod2->which(), PodUnion::Tag::F_ENUM);
 }