Make Dispatcher::Type an enum class.

mojo/edk/system/channel_endpoint_id.h

Index: mojo/edk/system/channel_endpoint_id.h
diff --git a/mojo/edk/system/channel_endpoint_id.h b/mojo/edk/system/channel_endpoint_id.h
index c67325878c6fbe3c69f0b1b8a600216ff3309064..afacb4e18cbe08b00f81325c2e942d55a67939f0 100644
--- a/mojo/edk/system/channel_endpoint_id.h
+++ b/mojo/edk/system/channel_endpoint_id.h
@@ -81,8 +81,9 @@ static_assert(sizeof(ChannelEndpointId) == sizeof(uint32_t),
               "ChannelEndpointId has incorrect size");
 
 // So logging macros and |DCHECK_EQ()|, etc. work.
-inline std::ostream& operator<<(std::ostream& out,
-                                const ChannelEndpointId& channel_endpoint_id) {
+MOJO_SYSTEM_IMPL_EXPORT inline std::ostream& operator<<(
+    std::ostream& out,
+    const ChannelEndpointId& channel_endpoint_id) {
   return out << channel_endpoint_id.value();
 }