Move the Dispatcher::EntrypointClass enum out of Dispatcher to its own file.

mojo/edk/system/message_pipe_dispatcher_unittest.cc

Index: mojo/edk/system/message_pipe_dispatcher_unittest.cc
diff --git a/mojo/edk/system/message_pipe_dispatcher_unittest.cc b/mojo/edk/system/message_pipe_dispatcher_unittest.cc
index 4bae64596b1ab18ed52d6f213ccab82da53cfe28..fa35f7ae7dd6a6f5455f1886b2392c01e98bc10c 100644
--- a/mojo/edk/system/message_pipe_dispatcher_unittest.cc
+++ b/mojo/edk/system/message_pipe_dispatcher_unittest.cc
@@ -180,13 +180,10 @@ TEST(MessagePipeDispatcherTest, SupportsEntrypointClass) {
     EXPECT_EQ(MOJO_RESULT_OK, d_peer->Close());
   }
 
-  EXPECT_TRUE(
-      d->SupportsEntrypointClass(Dispatcher::EntrypointClass::MESSAGE_PIPE));
-  EXPECT_FALSE(d->SupportsEntrypointClass(
-      Dispatcher::EntrypointClass::DATA_PIPE_PRODUCER));
-  EXPECT_FALSE(d->SupportsEntrypointClass(
-      Dispatcher::EntrypointClass::DATA_PIPE_CONSUMER));
-  EXPECT_FALSE(d->SupportsEntrypointClass(Dispatcher::EntrypointClass::BUFFER));
+  EXPECT_TRUE(d->SupportsEntrypointClass(EntrypointClass::MESSAGE_PIPE));
+  EXPECT_FALSE(d->SupportsEntrypointClass(EntrypointClass::DATA_PIPE_PRODUCER));
+  EXPECT_FALSE(d->SupportsEntrypointClass(EntrypointClass::DATA_PIPE_CONSUMER));
+  EXPECT_FALSE(d->SupportsEntrypointClass(EntrypointClass::BUFFER));
 
   // TODO(vtl): Check that it actually returns |MOJO_RESULT_INVALID_ARGUMENT|
   // for methods in unsupported entrypoint classes.