[parser] Improve parse error message for missing name in FunctionDeclaration

Added a new Error Message for Missing Function Name.

The program:

function(){}

...now produces:
	SyntaxError: Function statements require a valid function name.

...instead of:
	SyntaxError: Unexpected Token (

Bug: v8:3698, v8:6513
Change-Id: I3c12dfcfe80b94209aa9af434ae1d212970cf362
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1500914
Commit-Queue: Adam Klein <adamk@chromium.org>
Reviewed-by: Adam Klein <adamk@chromium.org>
Cr-Commit-Position: refs/heads/master@{#60376}

src/message-template.h

@@ -417,6 +417,7 @@ namespace internal {
   T(MalformedRegExp, "Invalid regular expression: /%/: %")                     \
   T(MalformedRegExpFlags, "Invalid regular expression flags")                  \
   T(ModuleExportUndefined, "Export '%' is not defined in module")              \
+  T(MissingFunctionName, "Function statements require a function name")        \
   T(HtmlCommentInModule, "HTML comments are not allowed in modules")           \
   T(MultipleDefaultsInSwitch,                                                  \
     "More than one default clause in switch statement")                        \

src/parsing/parser-base.h

@@ -3737,9 +3737,14 @@ ParserBase<Impl>::ParseHoistableDeclaration(
   IdentifierT name;
   FunctionNameValidity name_validity;
   IdentifierT variable_name;
-  if (default_export && peek() == Token::LPAREN) {
-    impl()->GetDefaultStrings(&name, &variable_name);
-    name_validity = kSkipFunctionNameCheck;
+  if (peek() == Token::LPAREN) {
+    if (default_export) {
+      impl()->GetDefaultStrings(&name, &variable_name);
+      name_validity = kSkipFunctionNameCheck;
+    } else {
+      ReportMessage(MessageTemplate::kMissingFunctionName);
+      return impl()->NullStatement();
+    }
   } else {
     bool is_strict_reserved = Token::IsStrictReservedWord(peek());
     name = ParseIdentifier();

test/message/fail/missing-function-name.js

+// Copyright 2019 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.
+
+function (){}

test/message/fail/missing-function-name.out

+*%(basename)s:5: SyntaxError: Function statements require a function name
+function (){}
+^^^^^^^^
+SyntaxError: Function statements require a function name

test/webkit/function-declaration-expected.txt

@@ -28,7 +28,7 @@ On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE
 
 PASS eval('function f(){return true;}') is undefined.
 PASS eval('function f(){return true;};f')() is true
-PASS eval('function(){return false;}')() threw exception SyntaxError: Unexpected token (.
+PASS eval('function(){return false;}')() threw exception SyntaxError: Function statements require a function name.
 PASS successfullyParsed is true
 
 TEST COMPLETE