ParserBase should accept ESCAPED_STRICT_RESERVED_WORD as an identifier

ParserBase::is_any_identifier currently does not recognise
Token::ESCAPED_STRICT_RESERVED_WORD as an identifier. This seems different
from what ParserBase::ParseIdentifierName does, and also prevents
"l\u0065t", unlike "let", from becoming a label.

This CL extends is_any_identifier to also accept ESCAPED_STRICT_RESERVED_WORD.

BUG=v8:5692

Review-Url: https://codereview.chromium.org/2695973003
Cr-Commit-Position: refs/heads/master@{#43204}

src/parsing/parser-base.h

@@ -811,6 +811,7 @@ class ParserBase {
   bool is_any_identifier(Token::Value token) {
     return token == Token::IDENTIFIER || token == Token::ENUM ||
            token == Token::AWAIT || token == Token::ASYNC ||
+           token == Token::ESCAPED_STRICT_RESERVED_WORD ||
            token == Token::FUTURE_STRICT_RESERVED_WORD || token == Token::LET ||
            token == Token::STATIC || token == Token::YIELD;
   }
@@ -1673,7 +1674,8 @@ ParserBase<Impl>::ParseIdentifierOrStrictReservedWord(
                                     !IsAsyncFunction(function_kind)) ||
       next == Token::ASYNC) {
     *is_strict_reserved = false;
-  } else if (next == Token::FUTURE_STRICT_RESERVED_WORD || next == Token::LET ||
+  } else if (next == Token::ESCAPED_STRICT_RESERVED_WORD ||
+             next == Token::FUTURE_STRICT_RESERVED_WORD || next == Token::LET ||
              next == Token::STATIC ||
              (next == Token::YIELD && !IsGeneratorFunction(function_kind))) {
     *is_strict_reserved = true;

test/cctest/test-parsing.cc

@@ -9449,3 +9449,20 @@ TEST(NoPessimisticContextAllocation) {
     }
   }
 }
+
+TEST(EscapedStrictReservedWord) {
+  // Test that identifiers which are both escaped and only reserved in the
+  // strict mode are accepted in non-strict mode.
+  const char* context_data[][2] = {{"", ""}, {NULL, NULL}};
+
+  const char* statement_data[] = {"if (true) l\u0065t: ;",
+                                  "function l\u0065t() { }",
+                                  "(function l\u0065t() { })",
+                                  "async function l\u0065t() { }",
+                                  "(async function l\u0065t() { })",
+                                  "l\u0065t => 42",
+                                  "async l\u0065t => 42",
+                                  NULL};
+
+  RunParserSyncTest(context_data, statement_data, kSuccess);
+}

test/mjsunit/regress/regress-5692.js

+// Copyright 2017 the V8 project authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// "let" in non-strict mode can be a label, even if composed of unicode escape
+// sequences.
+
+var wasTouched = false;
+l\u0065t:
+do {
+  break l\u0065t;
+  wasTouched = true;
+} while (false);
+// Verify that in addition to no exception thrown, breaking to the label also
+// works.
+assertFalse(wasTouched);