Add message sizing to basic IPC traits and struct macros.

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

 // Copyright 2015 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_NATIVE_SERIALIZATION_H_
 #define MOJO_PUBLIC_CPP_BINDINGS_LIB_NATIVE_SERIALIZATION_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 11 matching lines @@
 namespace internal {
 
 // Generated bindings for native-only types will specialize this to |true|.
 // It can be used as a signal (by e.g. the Array serializer) for when to use
 // SerializeNative_ with a type.
 template <typename E>
 struct ShouldUseNativeSerializer { static const bool value = false; };
 
 template <typename T>
 size_t GetSerializedSizeNative_(const T& value) {
-  return IPC::ParamTraits<T>::GetSize(value);
+  base::PickleSizer sizer;
+  IPC::ParamTraits<T>::GetSize(&sizer, value);
+  return sizer.payload_size();
 }
 
 template <typename T>
 void SerializeNative_(const T& value,
                       Buffer* buffer,
                       Array_Data<uint8_t>** out) {
   PickleBuffer* pickler = buffer->AsPickleBuffer();
   DCHECK(pickler) << "Native types can only be used with PickleBuffers.";
 
   ArrayHeader* header =
       reinterpret_cast<ArrayHeader*>(buffer->Allocate(sizeof(ArrayHeader)));
 
   // Remember where the Pickle started before writing.
   base::Pickle* pickle = pickler->pickle();
   const char* data_start = pickle->end_of_payload();
 
+#if !defined(NDEBUG) || defined(DCHECK_ALWAYS_ON)
+  size_t size_before_write = pickle->payload_size();
+#endif
+
   IPC::ParamTraits<T>::Write(pickle, value);
 
+#if !defined(NDEBUG) || defined(DCHECK_ALWAYS_ON)
+  DCHECK_GE(pickle->payload_size(), size_before_write);

[jam, 2016/02/04 18:34:01]

this is checking that the payload size didn't shrink? how could that ever
happen?

+  // Explicitly validate that the value returned by GetSize() always equals the
+  // number of bytes actually written by Write().
+  size_t bytes_written = pickle->payload_size() - size_before_write;
+  DCHECK_EQ(bytes_written, GetSerializedSizeNative_(value));
+#endif
+
   // Fix up the ArrayHeader so that num_elements contains the length of the
   // pickled data.
   size_t pickled_size = pickle->end_of_payload() - data_start;
   size_t total_size = pickled_size + sizeof(ArrayHeader);
   DCHECK_LT(total_size, std::numeric_limits<uint32_t>::max());
   header->num_bytes = static_cast<uint32_t>(total_size);
   header->num_elements = static_cast<uint32_t>(pickled_size);
 
   *out = reinterpret_cast<Array_Data<uint8_t>*>(header);
 }
@@ skipping 35 matching lines @@
   // Return the header to its original state.
   header->num_bytes += sizeof(ArrayHeader);
 
   return true;
 }
 
 }  // namespace internal
 }  // namespace mojo
 
 #endif  // MOJO_PUBLIC_CPP_BINDINGS_LIB_NATIVE_SERIALIZATION_H_