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

mojo/edk/system/platform_handle_dispatcher_unittest.cc

Index: mojo/edk/system/platform_handle_dispatcher_unittest.cc
diff --git a/mojo/edk/system/platform_handle_dispatcher_unittest.cc b/mojo/edk/system/platform_handle_dispatcher_unittest.cc
index e57c5112445b3b1c968580fe81b5c0fd5868e8f0..232c7df08787fc5334da5a534673e20898bf163b 100644
--- a/mojo/edk/system/platform_handle_dispatcher_unittest.cc
+++ b/mojo/edk/system/platform_handle_dispatcher_unittest.cc
@@ -74,13 +74,10 @@ TEST(PlatformHandleDispatcher, SupportsEntrypointClass) {
   ASSERT_TRUE(d);
   EXPECT_FALSE(h.is_valid());
 
-  EXPECT_FALSE(
-      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_FALSE(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.