Preliminary code for block scopes and block contexts.

src/ast.h

Index: src/ast.h
diff --git a/src/ast.h b/src/ast.h
index b4705f6ab853e2373bb66be3e4bee5b3044a7701..a735ee130d331feac5e633860920588c88a7ce89 100644
--- a/src/ast.h
+++ b/src/ast.h
@@ -359,9 +359,13 @@ class Block: public BreakableStatement {
   ZoneList<Statement*>* statements() { return &statements_; }
   bool is_initializer_block() const { return is_initializer_block_; }
 
+  Scope* block_scope() const { return block_scope_; }
+  void set_block_scope(Scope* block_scope) { block_scope_ = block_scope; }
+
  private:
   ZoneList<Statement*> statements_;
   bool is_initializer_block_;
+  Scope* block_scope_;
 };