Fix leak of message snapshot buffer when attempting to send an illegal object.

runtime/vm/dart_api_impl.cc

Index: runtime/vm/dart_api_impl.cc
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index 8ff2deb5d67f79af18fbb3ae1cc7074d99718e6e..38123f713854875c7fc62e68a45e23e7b5695f8d 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -1780,12 +1780,19 @@ DART_EXPORT bool Dart_HasLivePorts() {
 }
 
 
-static uint8_t* allocator(uint8_t* ptr, intptr_t old_size, intptr_t new_size) {
+static uint8_t* malloc_allocator(uint8_t* ptr,
+                                 intptr_t old_size,
+                                 intptr_t new_size) {
   void* new_ptr = realloc(reinterpret_cast<void*>(ptr), new_size);
   return reinterpret_cast<uint8_t*>(new_ptr);
 }
 
 
+static void malloc_deallocator(uint8_t* ptr) {
+  free(reinterpret_cast<void*>(ptr));
+}
+
+
 DART_EXPORT bool Dart_Post(Dart_Port port_id, Dart_Handle handle) {
   DARTSCOPE(Thread::Current());
   API_TIMELINE_DURATION;
@@ -1803,7 +1810,7 @@ DART_EXPORT bool Dart_Post(Dart_Port port_id, Dart_Handle handle) {
 
   const Object& object = Object::Handle(Z, raw_obj);
   uint8_t* data = NULL;
-  MessageWriter writer(&data, &allocator, false);
+  MessageWriter writer(&data, &malloc_allocator, &malloc_deallocator, false);
   writer.WriteMessage(object);
   intptr_t len = writer.BytesWritten();
   return PortMap::PostMessage(