Fix 56 hints in pkg/compiler

pkg/compiler/lib/src/universe/side_effects.dart

 // Copyright (c) 2013, 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 universe;
 
 class SideEffects {
   // Changes flags.
   static const int FLAG_CHANGES_INDEX = 0;
   static const int FLAG_CHANGES_INSTANCE_PROPERTY = FLAG_CHANGES_INDEX + 1;
@@ skipping 21 matching lines @@
     clearAllDependencies();
     clearAllSideEffects();
   }
 
   bool operator==(other) => _flags == other._flags;
 
   int get hashCode => throw new UnsupportedError('SideEffects.hashCode');
 
   bool _getFlag(int position) => (_flags & (1 << position)) != 0;
   void _setFlag(int position) { _flags |= (1 << position); }
-  bool _clearFlag(int position) { _flags &= ~(1 << position); }
+  void _clearFlag(int position) { _flags &= ~(1 << position); }
 
   int getChangesFlags() => _flags & ((1 << FLAG_CHANGES_COUNT) - 1);
   int getDependsOnFlags() {
     return (_flags & ((1 << FLAG_DEPENDS_ON_COUNT) - 1)) >> FLAG_CHANGES_COUNT;
   }
 
   bool hasSideEffects() => getChangesFlags() != 0;
   bool dependsOnSomething() => getDependsOnFlags() != 0;
 
   void setAllSideEffects() { _flags |= ((1 << FLAG_CHANGES_COUNT) - 1); }
@@ skipping 69 matching lines @@
     if (!dependsOnSomething()) buffer.write(' nothing');
     buffer.write(', Changes');
     if (changesIndex()) buffer.write(' []');
     if (changesInstanceProperty()) buffer.write(' field');
     if (changesStaticProperty()) buffer.write(' static');
     if (!hasSideEffects()) buffer.write(' nothing');
     buffer.write('.');
     return buffer.toString();
   }
 }