[runtime] Adding more detailed error message for Object::GetMethod.

src/js/weak-collection.js

Index: src/js/weak-collection.js
diff --git a/src/js/weak-collection.js b/src/js/weak-collection.js
index 0be714109e63b5a4500c53bf5ddfc8cf6be4f113..8ab038ecdcf0c1b522ac7bff00bad31b82a64d97 100644
--- a/src/js/weak-collection.js
+++ b/src/js/weak-collection.js
@@ -38,7 +38,7 @@ function WeakMapConstructor(iterable) {
   if (!IS_NULL_OR_UNDEFINED(iterable)) {
     var adder = this.set;
     if (!IS_CALLABLE(adder)) {
-      throw MakeTypeError(kPropertyNotFunction, 'set', this);
+      throw MakeTypeError(kPropertyNotFunction, adder, 'set', this);
     }
     for (var nextItem of iterable) {
       if (!IS_SPEC_OBJECT(nextItem)) {
@@ -127,7 +127,7 @@ function WeakSetConstructor(iterable) {
   if (!IS_NULL_OR_UNDEFINED(iterable)) {
     var adder = this.add;
     if (!IS_CALLABLE(adder)) {
-      throw MakeTypeError(kPropertyNotFunction, 'add', this);
+      throw MakeTypeError(kPropertyNotFunction, adder, 'add', this);
     }
     for (var value of iterable) {
       %_Call(adder, this, value);