Introduce object visitor to estimate the size of a native context.

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index ceadd4ed8b62776d355a0ea96f8efe2702cd444c..7f1000af5f7bc4ac35e936e65742836f223db99a 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -22,6 +22,7 @@
 #include "src/bootstrapper.h"
 #include "src/code-stubs.h"
 #include "src/compiler.h"
+#include "src/context-measure.h"
 #include "src/contexts.h"
 #include "src/conversions-inl.h"
 #include "src/counters.h"
@@ -5577,6 +5578,12 @@ void Context::SetErrorMessageForCodeGenerationFromStrings(Local<String> error) {
 }
 
 
+size_t Context::EstimatedSize() {
+  return static_cast<size_t>(
+      i::ContextMeasure(*Utils::OpenHandle(this)).Size());
+}
+
+
 MaybeLocal<v8::Object> ObjectTemplate::NewInstance(Local<Context> context) {
   PREPARE_FOR_EXECUTION(context, "v8::ObjectTemplate::NewInstance()", Object);
   auto self = Utils::OpenHandle(this);