Fix all Observatory warnings/errors.

runtime/observatory/lib/src/debugger/source_location.dart

 // Copyright (c) 2015, 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.
 
 part of debugger;
 
 class SourceLocation {
   SourceLocation.file(this.script, this.line, this.col);
   SourceLocation.func(this.function);
   SourceLocation.error(this.errorMessage);
@@ skipping 169 matching lines @@
               matches.add(cls);
             }
           }
         }
       }
       return matches;
     });
   }
 
   static ServiceFunction _getConstructor(Class cls, String name) {
-    var matches = [];
     for (var function in cls.functions) {
       assert(cls.loaded);
       if (name == function.name) {
         return function;
       }
     }
     return null;
   }
 
   // TODO(turnidge): This does not handle named functions which are
@@ skipping 157 matching lines @@
     return 'invalid source location (${errorMessage})';
   }
 
   Script script;
   int line;
   int col;
   ServiceFunction function;
   String errorMessage;
   bool get valid => (errorMessage == null);
 }