Do not use C++ const references in the C interface.

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index a073b8f8fc98b66e57999c3d461187ed26f3abae..601b9780b02dfd407e31b466b2ec7fe79f75ff05 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -305,7 +305,7 @@ uword Api::Reallocate(uword ptr, intptr_t old_size, intptr_t new_size) {
 // --- Handles ---
 
 
-DART_EXPORT bool Dart_IsError(const Dart_Handle& handle) {
+DART_EXPORT bool Dart_IsError(Dart_Handle handle) {
   DARTSCOPE(Isolate::Current());
   const Object& obj = Object::Handle(Api::UnwrapHandle(handle));
   return obj.IsApiError();
@@ -340,7 +340,7 @@ static const char* MakeUnhandledExceptionCString(
 }
 
 
-DART_EXPORT const char* Dart_GetError(const Dart_Handle& handle) {
+DART_EXPORT const char* Dart_GetError(Dart_Handle handle) {
   DARTSCOPE(Isolate::Current());
 
   const Object& obj = Object::Handle(Api::UnwrapHandle(handle));