Add support for medium integers to the native message format

runtime/vm/dart_api_message.cc

Index: runtime/vm/dart_api_message.cc
diff --git a/runtime/vm/dart_api_message.cc b/runtime/vm/dart_api_message.cc
index d5f2e69d77bd4af57603a0de4fb1e5e0daa59104..3624242d25aab309b5bec2ead99351ed60b64600 100644
--- a/runtime/vm/dart_api_message.cc
+++ b/runtime/vm/dart_api_message.cc
@@ -81,6 +81,13 @@ Dart_CObject* ApiMessageReader::AllocateDartCObjectInt32(int32_t val) {
 }
 
 
+Dart_CObject* ApiMessageReader::AllocateDartCObjectInt64(int64_t val) {
+  Dart_CObject* value = AllocateDartCObject(Dart_CObject::kInt64);
+  value->value.as_int64 = val;
+  return value;
+}
+
+
 Dart_CObject* ApiMessageReader::AllocateDartCObjectDouble(double val) {
   Dart_CObject* value = AllocateDartCObject(Dart_CObject::kDouble);
   value->value.as_double = val;
@@ -190,6 +197,15 @@ Dart_CObject* ApiMessageReader::ReadInlinedObject(intptr_t object_id) {
       return value;
       break;
     }
+    case ObjectStore::kMintClass: {
+      int64_t value = Read<int64_t>();
+      if (kMinInt32 <= value && value <= kMaxInt32) {
+        return AllocateDartCObjectInt32(value);
+      } else {
+        return AllocateDartCObjectInt64(value);
+      }
+      break;
+    }
     case ObjectStore::kDoubleClass: {
       // Read the double value for the object.
       Dart_CObject* object = AllocateDartCObjectDouble(Read<double>());