[mojo] Use base::Pickle for Message storage.

mojo/public/cpp/bindings/tests/validation_unittest.cc

 // 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.
 
 #include <stdio.h>
 
 #include <algorithm>
 #include <string>
 #include <vector>
 
@@ skipping 132 matching lines @@
                   std::string* expected) {
   std::vector<uint8_t> data;
   size_t num_handles;
   if (!ReadAndParseDataFile(GetPath(test, ".data"), &data, &num_handles) ||
       !ReadResultFile(GetPath(test, ".expected"), expected)) {
     return false;
   }
 
   message->AllocUninitializedData(static_cast<uint32_t>(data.size()));
   if (!data.empty())
-    memcpy(message->mutable_data(), &data[0], data.size());
+    memcpy(message->buffer()->Allocate(data.size()), &data[0], data.size());
   message->mutable_handles()->resize(num_handles);
 
   return true;
 }
 
 void RunValidationTests(const std::string& prefix,
                         MessageReceiver* test_message_receiver) {
   std::vector<std::string> names =
       EnumerateSourceRootRelativeDirectory(GetPath("", ""));
   std::vector<std::string> tests = GetMatchingTests(names, prefix);
@@ skipping 319 matching lines @@
       static_cast<StructWithEnum::EnumWithin>(2)));
   EXPECT_TRUE(StructWithEnum::EnumWithin_IsValidValue(
       static_cast<StructWithEnum::EnumWithin>(3)));
   EXPECT_FALSE(StructWithEnum::EnumWithin_IsValidValue(
       static_cast<StructWithEnum::EnumWithin>(4)));
 }
 
 }  // namespace
 }  // namespace test
 }  // namespace mojo