[ast] Never declare non-lexical variables as kNeedsInitialization.

src/ast/variables.h

Index: src/ast/variables.h
diff --git a/src/ast/variables.h b/src/ast/variables.h
index 950db3c0021263f93209609d24cfd61de8a2d58f..9dae9e634abdf59d2123893b52d20919aa96e91f 100644
--- a/src/ast/variables.h
+++ b/src/ast/variables.h
@@ -73,6 +73,8 @@ class Variable: public ZoneObject {
   bool is_dynamic() const { return IsDynamicVariableMode(mode_); }
   bool is_const_mode() const { return IsImmutableVariableMode(mode_); }
   bool binding_needs_init() const {
+    DCHECK(initialization_flag_ != kNeedsInitialization ||
+           IsLexicalVariableMode(mode_));
     return initialization_flag_ == kNeedsInitialization;
   }