(early draft) Strict mode - throw exception on assignment to read only property.

src/ic-inl.h

Index: src/ic-inl.h
diff --git a/src/ic-inl.h b/src/ic-inl.h
index 8fbc18436dd2a395db691f9d815fa39ed822c1c5..9d358eddb31a3dc887078c4ce784e0aff4d3fe6f 100644
--- a/src/ic-inl.h
+++ b/src/ic-inl.h
@@ -76,6 +76,15 @@ Code* IC::GetTargetAtAddress(Address address) {
 
 void IC::SetTargetAtAddress(Address address, Code* target) {
   ASSERT(target->is_inline_cache_stub() || target->is_compare_ic_stub());
+#ifdef DEBUG
+  // STORE_IC and KEYED_STORE_IC use Code::extra_ic_state() to mark
+  // ICs as strict mode. The strict-ness of the IC must be preserved.
+  Code* old_target = GetTargetAtAddress(address);
+  if (old_target->kind() == Code::STORE_IC ||
+      old_target->kind() == Code::KEYED_STORE_IC) {
+    ASSERT(old_target->extra_ic_state() == target->extra_ic_state());
+  }
+#endif
   Assembler::set_target_address_at(address, target->instruction_start());
 }