mojom: Add associative arrays to the mojom language.

mojo/public/cpp/bindings/lib/validate_params.h

+// Copyright 2014 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.
+
+#ifndef MOJO_PUBLIC_CPP_BINDINGS_LIB_VALIDATE_PARAMS_H_
+#define MOJO_PUBLIC_CPP_BINDINGS_LIB_VALIDATE_PARAMS_H_
+
+namespace mojo {
+namespace internal {
+
+// Array type information needed for valdiation.
+template <uint32_t in_expected_num_elements,
+          bool in_element_is_nullable,
+          typename InElementValidateParams>
+class ArrayValidateParams {
+ public:
+  // Validation information for elements. It is either another specialization
+  // of ArrayValidateParams (if elements are arrays, or the value type of a map

[yzshen1, 2014/10/09 17:41:58]

In the map case, ElementValidateParams is for the "value array", it is not for
the "elements of the value array". Therefore, whether the value type of a map is
arrays is one level deeper.

So I think this should be "if elements are arrays or maps. In the case of maps,
this is used to validate the value array" or something like that.

+  // is arrays) or NoValidateParams.
+  typedef InElementValidateParams ElementValidateParams;
+
+  // If |expected_num_elements| is not 0, the array is expected to have exactly
+  // that number of elements.
+  static const uint32_t expected_num_elements = in_expected_num_elements;
+  // Whether the elements are nullable.
+  static const bool element_is_nullable = in_element_is_nullable;
+};
+
+// NoValidateParams is used to indicate the end of an ArrayValidateParams chain.
+class NoValidateParams {};
+
+}  // namespace internal
+}  // namespace mojo
+
+#endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_VALIDATE_PARAMS_H_