Mojo C++ bindings: Fix bug: array<>, map<> should only initialize elements if they're not null when…

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

 // 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.
 
 #ifndef MOJO_PUBLIC_CPP_BINDINGS_LIB_BINDINGS_INTERNAL_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_BINDINGS_INTERNAL_H_
 
 #include <type_traits>
 
 #include "mojo/public/cpp/bindings/lib/template_util.h"
@@ skipping 180 matching lines @@
 // TODO(vardhan): Instead of providing |move_only| & |is_union| template
 // parameters, provide a default "typename Enable = void" template parameter,
 // and have specializations define their own Enable expressions (similar to how
 // ValueTraits is).
 template <typename T,
           bool move_only = IsMoveOnlyType<T>::value,
           bool is_union =
               IsUnionWrapperType<typename RemoveStructPtr<T>::type>::value>
 struct WrapperTraits;
 
+// Catch-all for all mojom types not specialized below.
 template <typename T>
 struct WrapperTraits<T, false, false> {
   using DataType = T;
 };
 template <typename H>
 struct WrapperTraits<ScopedHandleBase<H>, true, false> {
   using DataType = H;
 };
 template <typename I>
 struct WrapperTraits<InterfaceRequest<I>, true, false> {
   using DataType = MessagePipeHandle;
 };
 template <typename Interface>
 struct WrapperTraits<InterfacePtr<Interface>, true, false> {
   using DataType = Interface_Data;
 };
+// Unions.
 template <typename U>
 struct WrapperTraits<StructPtr<U>, true, true> {
   using DataType = typename U::Data_;
 };
 template <typename U>
 struct WrapperTraits<InlinedStructPtr<U>, true, true> {
   using DataType = typename U::Data_;
 };
+// Catch-all for other pointer types: arrays, maps.
 template <typename S>
 struct WrapperTraits<S, true, false> {
   using DataType = typename S::Data_*;
 };
 
 template <typename T, typename Enable = void>
 struct ValueTraits {
   static bool Equals(const T& a, const T& b) { return a == b; }
 };
 
@@ skipping 31 matching lines @@
   static bool Equals(const InterfaceRequest<I>& a,
                      const InterfaceRequest<I>& b) {
     return (&a == &b) || (!a.is_pending() && !b.is_pending());
   }
 };
 
 }  // namespace internal
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_BINDINGS_INTERNAL_H_