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If allow_string_plus is set to false, the compiler will report an error when it finds a string literal followed by +. Invoking the + operator on a string value throws a noSuchMethod exception. This is temporary code that we'll eliminate once the + operator on strings is completely removed. Review URL: https://chromiumcodereview.appspot.com//9960084 git-svn-id: https://dart.googlecode.com/svn/branches/bleeding_edge/dart@6423 260f80e4-7a28-3924-810f-c04153c831b5