Mojo cpp bindings: report the reason of validation failure.

mojo/public/cpp/bindings/lib/array_internal.cc

 // Copyright 2013 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 "mojo/public/cpp/bindings/lib/array_internal.h"
 
 namespace mojo {
 namespace internal {
 
 ArrayDataTraits<bool>::BitRef::~BitRef() {
@@ skipping 40 matching lines @@
   for (uint32_t i = 0; i < header->num_elements; ++i)
     DecodeHandle(&elements[i], handles);
 }
 
 // static
 bool ArraySerializationHelper<Handle, true>::ValidateElements(
     const ArrayHeader* header,
     const ElementType* elements,
     BoundsChecker* bounds_checker) {
   for (uint32_t i = 0; i < header->num_elements; ++i) {
-    if (!bounds_checker->ClaimHandle(elements[i]))
+    if (!bounds_checker->ClaimHandle(elements[i])) {
+      ReportValidationError(VALIDATION_ERROR_ILLEGAL_HANDLE);
       return false;
+    }
   }
   return true;
 }
 
 }  // namespace internal
 }  // namespace mojo