[parser] avoid for-loop desugaring unless loop var may be captured

In https://chromium-review.googlesource.com/c/472247/, I avoided
running DesugarLexicalBindingsInForStatement() if there were no lexical
loop variables, the function was not resumable, and the variables are
not captured by eval or a function declaration.

I think it's now possible to limit this further, and only do the more
extensive desugaring if there's a function declaration / eval() call
in the loop body. `yield` and `await` are not an issue as those loop
variables are written to the register file and not lost.

This change just removes the `is_resumable()` condition. If it passes
tests, I think it's safe.

BUG=v8:4762, v8:5460, v8:6579

Change-Id: I92d0308ad9401c1338411bc9ae9021f978803d3a
Reviewed-on: https://chromium-review.googlesource.com/563587
Commit-Queue: Caitlin Potter <caitp@igalia.com>
Reviewed-by: Georg Neis <neis@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#46536}

src/parsing/parser-base.h

@@ -5830,7 +5830,7 @@ typename ParserBase<Impl>::StatementT ParserBase<Impl>::ParseStandardForLoop(
   scope()->set_end_position(scanner()->location().end_pos);
   inner_scope->set_end_position(scanner()->location().end_pos);
   if (bound_names_are_lexical && for_info->bound_names.length() > 0 &&
-      (is_resumable() || function_state_->contains_function_or_eval())) {
+      function_state_->contains_function_or_eval()) {
     scope()->set_is_hidden();
     return impl()->DesugarLexicalBindingsInForStatement(
         loop, init, cond, next, body, body_range, inner_scope, *for_info,

test/debugger/debug/debug-scopes-suspended-generators.js

@@ -276,13 +276,14 @@ function *gen10() {
 g = gen10();
 g.next();
 CheckScopeChain([debug.ScopeType.Block,
+                 debug.ScopeType.Block,
                  debug.ScopeType.Local,
                  debug.ScopeType.Script,
                  debug.ScopeType.Global], g);
-CheckScopeContent({i: 0}, 0, g);
+CheckScopeContent({i: 0}, 1, g);
 
 g.next();
-CheckScopeContent({i: 1}, 0, g);
+CheckScopeContent({i: 1}, 1, g);
 
 // Nested generators.