[ast] Mark temporaries as maybe-assigned by default.

src/parsing/parser.cc

Index: src/parsing/parser.cc
diff --git a/src/parsing/parser.cc b/src/parsing/parser.cc
index b9d26995f1b1e19078b93de222c03bd16f08de64..d0e0e999213b83c013713dce70727e3a84d175d2 100644
--- a/src/parsing/parser.cc
+++ b/src/parsing/parser.cc
@@ -2991,7 +2991,7 @@ Block* Parser::BuildRejectPromiseOnException(Block* inner_block) {
         Context::ASYNC_FUNCTION_PROMISE_CREATE_INDEX,
         new (zone()) ZoneList<Expression*>(0, zone()), kNoSourcePosition);
     Assignment* assign_promise = factory()->NewAssignment(
-        Token::INIT, factory()->NewVariableProxy(PromiseVariable()),
+        Token::ASSIGN, factory()->NewVariableProxy(PromiseVariable()),
         create_promise, kNoSourcePosition);
     set_promise =
         factory()->NewExpressionStatement(assign_promise, kNoSourcePosition);