Make mash register initial batch of accelerators in single shot.

services/ui/ws/event_dispatcher.cc

Index: services/ui/ws/event_dispatcher.cc
diff --git a/services/ui/ws/event_dispatcher.cc b/services/ui/ws/event_dispatcher.cc
index 18d3dafec9e8931a6c7d07153eea00cb36ce9e12..4dbe448996862dce7d1be8a1f8a3d88d18308311 100644
--- a/services/ui/ws/event_dispatcher.cc
+++ b/services/ui/ws/event_dispatcher.cc
@@ -252,10 +252,24 @@ void EventDispatcher::UpdateCursorProviderByLastKnownLocation() {
 bool EventDispatcher::AddAccelerator(uint32_t id,
                                      mojom::EventMatcherPtr event_matcher) {
   std::unique_ptr<Accelerator> accelerator(new Accelerator(id, *event_matcher));
+
   // If an accelerator with the same id or matcher already exists, then abort.
+  bool is_duplicate = false;
+  std::string error_message;
   for (const auto& pair : accelerators_) {
-    if (pair.first == id || accelerator->EqualEventMatcher(pair.second.get()))
+    if (pair.first == id) {
+      error_message = "Duplicate accelerator id.";
+      is_duplicate = true;
+    } else if (accelerator->EqualEventMatcher(pair.second.get())) {
+      error_message = "Duplicate accelerator matcher.";
+      is_duplicate = true;
+    }
+    if (is_duplicate) {
+      LOG(ERROR) << error_message << " accelerator id=" << accelerator->id()
+                 << " type=" << event_matcher->type_matcher->type
+                 << " flags=" << event_matcher->flags_matcher->flags;
       return false;
+    }
   }
   accelerators_.insert(Entry(id, std::move(accelerator)));
   return true;