IME for Mus: Fix InputMethodMusTest.DispatchKeyEvent's deadlock.

services/ui/ime/ime_server_impl.cc

Index: services/ui/ime/ime_server_impl.cc
diff --git a/services/ui/ime/ime_server_impl.cc b/services/ui/ime/ime_server_impl.cc
index 3f3405fdb3966699248dade91cb9c28474a1cb41..9cae996ec9e009f9509c5a9c838ad410eff7ef72 100644
--- a/services/ui/ime/ime_server_impl.cc
+++ b/services/ui/ime/ime_server_impl.cc
@@ -35,6 +35,12 @@ void IMEServerImpl::AddBinding(mojom::IMEServerRequest request) {
 }
 
 void IMEServerImpl::OnDriverChanged(mojom::IMEDriverPtr driver) {
+  // TODO(moshayedi): crbug.com/669681. Handle switching drivers properly. For
+  // now we only register the first driver to avoid clients of the previous
+  // driver from hanging.
+  if (driver_)
+    return;
+
   // TODO(moshayedi): crbug.com/664267. Make sure this is the driver we
   // requested at OnGotCatalogEntries().
   driver_ = std::move(driver);