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

runtime/lib/vmservice.cc

Index: runtime/lib/vmservice.cc
diff --git a/runtime/lib/vmservice.cc b/runtime/lib/vmservice.cc
index 5b6af4f707ce598da661873e44ac8f1b94610d15..9d83c13b9d8e421a7bb7b734f77843d561c7e655 100644
--- a/runtime/lib/vmservice.cc
+++ b/runtime/lib/vmservice.cc
@@ -21,11 +21,17 @@ namespace dart {
 
 DECLARE_FLAG(bool, trace_service);
 
-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));
+}
+
 
 #ifndef PRODUCT
 class RegisterRunningIsolatesVisitor : public IsolateVisitor {
@@ -95,7 +101,7 @@ DEFINE_NATIVE_ENTRY(VMService_SendIsolateServiceMessage, 2) {
 
   // Serialize message.
   uint8_t* data = NULL;
-  MessageWriter writer(&data, &allocator, false);
+  MessageWriter writer(&data, &malloc_allocator, &malloc_deallocator, false);
   writer.WriteMessage(message);
 
   // TODO(turnidge): Throw an exception when the return value is false?