Fix 56 hints in pkg/compiler

pkg/compiler/lib/src/string_validator.dart

 // Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 // Check the validity of string literals.
 
 library stringvalidator;
 
 import "dart:collection";
 
@@ skipping 30 matching lines @@
     int quoteChar = source.current;
     if (quoteChar == $r) {
       raw = true;
       source.moveNext();
       quoteChar = source.current;
     }
     assert(quoteChar == $SQ || quoteChar == $DQ);
     // String has at least one quote. Check it if has three.
     // If it only has two, the string must be an empty string literal,
     // and end after the second quote.
-    bool multiline = false;
     if (source.moveNext() && source.current == quoteChar && source.moveNext()) {
       int code = source.current;
       assert(code == quoteChar);  // If not, there is a bug in the parser.
       leftQuoteLength = 3;
 
       // Check if a multiline string starts with optional whitespace followed by
       // a newline (CR, LF or CR+LF).
       // We also accept if the these characters are escaped by a backslash.
       int newLineLength = 1;
       while (true) {
@@ skipping 86 matching lines @@
             code = iter.next();
             if (!isHexDigit(code)) {
               stringParseError("Invalid character in escape sequence",
                                token, index);
               return null;
             }
           }
           // A two-byte hex escape can't generate an invalid value.
           continue;
         } else if (code == $u) {
-          int escapeStart = index - 1;
           index++;
           code = iter.hasNext ? iter.next() : 0;
           int value = 0;
           if (code == $OPEN_CURLY_BRACKET) {
             // expect 1-6 hex digits.
             int count = 0;
             while (iter.hasNext) {
               code = iter.next();
               index++;
               if (code == $CLOSE_CURLY_BRACKET) {
@@ skipping 57 matching lines @@
       return null;
     }
     // String literal successfully validated.
     if (quoting.raw || !containsEscape) {
       // A string without escapes could just as well have been raw.
       return new DartString.rawString(string, length);
     }
     return new DartString.escapedString(string, length);
   }
 }