[parser] Skipping inner funcs: Fix bailout.

When the bailout triggered, we assumed we're generating data (i.e., we're inside
a non-arrow function). This is not true; it's possible that we're already inside
an arrow function and not generating data anyway.

BUG=v8:5516,chromium:761980

Change-Id: Iad9c8dde283031630953ef9a46c1e68bc0cee048
Reviewed-on: https://chromium-review.googlesource.com/655081Reviewed-by: Adam Klein <adamk@chromium.org>
Commit-Queue: Marja Hölttä <marja@chromium.org>
Cr-Commit-Position: refs/heads/master@{#47905}

src/parsing/preparser.cc

@@ -374,8 +374,8 @@ PreParserStatement PreParser::BuildParameterInitializationBlock(
   DCHECK(!parameters.is_simple);
   DCHECK(scope()->is_function_scope());
   if (FLAG_preparser_scope_analysis &&
-      scope()->AsDeclarationScope()->calls_sloppy_eval()) {
-    DCHECK_NOT_NULL(produced_preparsed_scope_data_);
+      scope()->AsDeclarationScope()->calls_sloppy_eval() &&
+      produced_preparsed_scope_data_ != nullptr) {
     // We cannot replicate the Scope structure constructed by the Parser,
     // because we've lost information whether each individual parameter was
     // simple or not. Give up trying to produce data to skip inner functions.

test/mjsunit/skipping-inner-functions-bailout.js

@@ -76,3 +76,9 @@ function TestMultiBailout3() {
   function not_skippable_either() {}
 }
 TestMultiBailout3();
+
+// Regression test for
+// https://bugs.chromium.org/p/chromium/issues/detail?id=761980. The conditions
+// triggering a bailout occur in a context where we're not generating data
+// anyway (inside an arrow function). (This needs to be at top level.)
+x => { (y=eval()) => {} }