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

test/cctest/test-api.cc

Index: test/cctest/test-api.cc
diff --git a/test/cctest/test-api.cc b/test/cctest/test-api.cc
index ef98faf711c97807e8d899710a793c0f043a8d20..78800d45cee5ff353309b8eb4074e504d6489238 100644
--- a/test/cctest/test-api.cc
+++ b/test/cctest/test-api.cc
@@ -21827,3 +21827,11 @@ TEST(FutexInterruption) {
       "Atomics.futexWait(i32a, 0, 0);");
   CHECK(try_catch.HasTerminated());
 }
+
+
+TEST(EstimatedContextSize) {
+  v8::Isolate* isolate = CcTest::isolate();
+  v8::HandleScope scope(isolate);
+  LocalContext env;
+  CHECK(50000 < env->EstimatedSize());
+}