[generators] Desugar yield*.

src/parsing/rewriter.cc

Index: src/parsing/rewriter.cc
diff --git a/src/parsing/rewriter.cc b/src/parsing/rewriter.cc
index 4da60aca186589015a2e9ba2fca76f0943d54714..3477026477ace60c42c732c7ac94aea911a8c700 100644
--- a/src/parsing/rewriter.cc
+++ b/src/parsing/rewriter.cc
@@ -225,6 +225,7 @@ void Processor::VisitTryFinallyStatement(TryFinallyStatement* node) {
      // at the end again: ".backup = .result; ...; .result = .backup"
      // This is necessary because the finally block does not normally contribute
      // to the completion value.
+    CHECK(scope() != nullptr);
     Variable* backup = scope()->NewTemporary(
         factory()->ast_value_factory()->dot_result_string());
     Expression* backup_proxy = factory()->NewVariableProxy(backup);