Fix pre-parsing of 'use strict' directive after string literals.

src/preparser.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 426 matching lines @@
           return Statement(kUseStrictExpressionStatement);
         }
         if (expression.IsStringLiteral()) {
           return Statement(kStringLiteralExpressionStatement);
         }
       }
       return Default();
     }
 
     bool IsStringLiteral() {
-      return code_ != kUnknownStatement;
+      return code_ == kStringLiteralExpressionStatement;
     }
 
     bool IsUseStrictLiteral() {
       return code_ == kUseStrictExpressionStatement;
     }
 
     bool IsFunctionDeclaration() {
       return code_ == kFunctionDeclaration;
     }
 
@@ skipping 231 matching lines @@
   bool allow_generators_;
   bool allow_for_of_;
   bool parenthesized_function_;
 
   friend class i::ObjectLiteralChecker<PreParser>;
 };
 
 } }  // v8::preparser
 
 #endif  // V8_PREPARSER_H