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

mojo/public/cpp/bindings/struct_ptr.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_STRUCT_PTR_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_STRUCT_PTR_H_
 
 #include <new>
 
 #include "mojo/public/cpp/bindings/type_converter.h"
 #include "mojo/public/cpp/environment/logging.h"
 #include "mojo/public/cpp/system/macros.h"
 
 namespace mojo {
 namespace internal {
 
 template <typename Struct>
 class StructHelper {
  public:
   template <typename Ptr>
   static void Initialize(Ptr* ptr) {
     ptr->Initialize();
   }
 };
 
 }  // namespace internal
 
-// Smart pointer wrapping a mojom structure with move-only semantics.
+// Smart pointer wrapping a mojom structure or union, with move-only semantics.
 template <typename Struct>
 class StructPtr {
  public:
-
   StructPtr() : ptr_(nullptr) {}
   StructPtr(decltype(nullptr)) : ptr_(nullptr) {}
 
   ~StructPtr() { delete ptr_; }
 
   StructPtr& operator=(decltype(nullptr)) {
     reset();
     return *this;
   }
 
@@ skipping 53 matching lines @@
   void Take(StructPtr* other) {
     reset();
     Swap(other);
   }
 
   Struct* ptr_;
 
   MOJO_MOVE_ONLY_TYPE(StructPtr);
 };
 
-// Designed to be used when Struct is small and copyable.
+// Designed to be used when Struct is small and copyable. Unions are always
+// InlinedStructPtr in practice.
 template <typename Struct>
 class InlinedStructPtr {
  public:
-
   InlinedStructPtr() : is_null_(true) {}
   InlinedStructPtr(decltype(nullptr)) : is_null_(true) {}
 
   ~InlinedStructPtr() {}
 
   InlinedStructPtr& operator=(decltype(nullptr)) {
     reset();
     return *this;
   }
 
@@ skipping 54 matching lines @@
 
   mutable Struct value_;
   bool is_null_;
 
   MOJO_MOVE_ONLY_TYPE(InlinedStructPtr);
 };
 
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_STRUCT_PTR_H_