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

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

Index: mojo/public/cpp/bindings/tests/validation_unittest.cc
diff --git a/mojo/public/cpp/bindings/tests/validation_unittest.cc b/mojo/public/cpp/bindings/tests/validation_unittest.cc
index f3ff9abc21b896146c261310ab9041a555d4ac14..7153a59ae9e301c63b6352717897189ec1a9b831 100644
--- a/mojo/public/cpp/bindings/tests/validation_unittest.cc
+++ b/mojo/public/cpp/bindings/tests/validation_unittest.cc
@@ -148,9 +148,10 @@ bool ReadTestCase(const std::string& test,
     return false;
   }
 
-  message->AllocUninitializedData(static_cast<uint32_t>(data.size()));
+  message->Initialize(static_cast<uint32_t>(data.size()),
+                      false /* zero_initialized */);
   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;