Object.observe: implement map bit and functions to access it.

src/objects-inl.h

Index: src/objects-inl.h
diff --git a/src/objects-inl.h b/src/objects-inl.h
index 4e7d8f8c08702943ef60fb3692b5ceb56482ec5d..640ca5e498e13feb7bc68a1a3dc0d093736f81bf 100644
--- a/src/objects-inl.h
+++ b/src/objects-inl.h
@@ -3151,6 +3151,16 @@ bool Map::owns_descriptors() {
 }
 
 
+void Map::set_is_observed(bool is_observed) {
+  set_bit_field3(IsObserved::update(bit_field3(), is_observed));
+}
+
+
+bool Map::is_observed() {
+  return IsObserved::decode(bit_field3());
+}
+
+
 void Code::set_flags(Code::Flags flags) {
   STATIC_ASSERT(Code::NUMBER_OF_KINDS <= KindField::kMax + 1);
   // Make sure that all call stubs have an arguments count.