Preparsing inner funcs: declare arguments for preparsed scopes

This makes maybe_assigned correct (instead of being overly pessimistic
in the following case):

function f() { function g() { arguments; }; }

(Tests upcoming as part of https://codereview.chromium.org/2580833005 )

BUG=v8:5501, v8:5678
R=verwaest@chromium.org, neis@chromium.org

Review-Url: https://codereview.chromium.org/2579303002
Cr-Commit-Position: refs/heads/master@{#41787}

src/parsing/preparser.cc

@@ -131,11 +131,19 @@ PreParser::PreParseResult PreParser::PreParseFunction(
         formals_end_position, CHECK_OK_VALUE(kPreParseSuccess));
     has_duplicate_parameters =
         !classifier()->is_valid_formal_parameter_list_without_duplicates();
+
+    if (track_unresolved_variables_) {
+      function_scope->DeclareVariableName(
+          ast_value_factory()->arguments_string(), VAR);
+      function_scope->DeclareVariableName(ast_value_factory()->this_string(),
+                                          VAR);
+    }
   }
 
   Expect(Token::LBRACE, CHECK_OK_VALUE(kPreParseSuccess));
   LazyParsingResult result = ParseStatementListAndLogFunction(
       &formals, has_duplicate_parameters, may_abort, ok);
+
   use_counts_ = nullptr;
   track_unresolved_variables_ = false;