exo: Produce an error if stylus delegate is already associated.

components/exo/wayland/server.cc

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "components/exo/wayland/server.h"
 
 #include <grp.h>
 #include <linux/input.h>
 #include <stddef.h>
 #include <stdint.h>
@@ skipping 2939 matching lines @@
     pointer_stylus_destroy};
 
 ////////////////////////////////////////////////////////////////////////////////
 // stylus interface:
 
 void stylus_get_pointer_stylus(wl_client* client,
                                wl_resource* resource,
                                uint32_t id,
                                wl_resource* pointer_resource) {
   Pointer* pointer = GetUserDataAs<Pointer>(pointer_resource);
+  if (pointer->HasStylusDelegate()) {
+    wl_resource_post_error(
+        resource, ZCR_STYLUS_V1_ERROR_POINTER_STYLUS_EXISTS,
+        "pointer has already been associated with a stylus object");
+    return;
+  }
 
   wl_resource* stylus_resource =
       wl_resource_create(client, &zcr_pointer_stylus_v1_interface, 1, id);
 
   SetImplementation(
       stylus_resource, &pointer_stylus_implementation,
       base::MakeUnique<WaylandPointerStylusDelegate>(stylus_resource, pointer));
 }
 
 const struct zcr_stylus_v1_interface stylus_implementation = {
@@ skipping 39 matching lines @@
   wl_global_create(wl_display_.get(), &wp_viewporter_interface, 1, display_,
                    bind_viewporter);
   wl_global_create(wl_display_.get(), &zcr_secure_output_v1_interface, 1,
                    display_, bind_secure_output);
   wl_global_create(wl_display_.get(), &zcr_alpha_compositing_v1_interface, 1,
                    display_, bind_alpha_compositing);
   wl_global_create(wl_display_.get(), &zcr_remote_shell_v1_interface,
                    remote_shell_version, display_, bind_remote_shell);
   wl_global_create(wl_display_.get(), &zcr_gaming_input_v1_interface, 1,
                    display_, bind_gaming_input);
-  wl_global_create(wl_display_.get(), &zcr_stylus_v1_interface, 1, display_,
+  wl_global_create(wl_display_.get(), &zcr_stylus_v1_interface, 2, display_,
                    bind_stylus);
 }
 
 Server::~Server() {}
 
 // static
 std::unique_ptr<Server> Server::Create(Display* display) {
   std::unique_ptr<Server> server(new Server(display));
 
   char* runtime_dir = getenv("XDG_RUNTIME_DIR");
@@ skipping 52 matching lines @@
   DCHECK(event_loop);
   wl_event_loop_dispatch(event_loop, timeout.InMilliseconds());
 }
 
 void Server::Flush() {
   wl_display_flush_clients(wl_display_.get());
 }
 
 }  // namespace wayland
 }  // namespace exo