Fix LookupCode for the DatePrototype_GetField builtin

src/frames-inl.h

Index: src/frames-inl.h
diff --git a/src/frames-inl.h b/src/frames-inl.h
index 77784b823459e478139363da86cd462e64782cf3..61d0dcd66374feb66bef36bae6e719a9d5ecc920 100644
--- a/src/frames-inl.h
+++ b/src/frames-inl.h
@@ -63,6 +63,8 @@ inline StackHandler* StackFrame::top_handler() const {
 
 
 inline Code* StackFrame::LookupCode() const {
+  // TODO(jgruber): This should really check that pc is within the returned
+  // code's instruction range [instruction_start(), instruction_end()[.
   return GetContainingCode(isolate(), pc());
 }