Expose a lower bound of malloc'd memory via heap statistics

src/json-parser.h

Index: src/json-parser.h
diff --git a/src/json-parser.h b/src/json-parser.h
index 5693933ee0b927575e9961da02427684b07c2980..1b9829fa40ba39774656836ad1c8941b36ab3be3 100644
--- a/src/json-parser.h
+++ b/src/json-parser.h
@@ -37,6 +37,7 @@ class JsonParser BASE_EMBEDDED {
         source_length_(source->length()),
         isolate_(source->map()->GetHeap()->isolate()),
         factory_(isolate_->factory()),
+        zone_(isolate_->allocator()),
         object_constructor_(isolate_->native_context()->object_function(),
                             isolate_),
         position_(-1) {