Fix deprecation warnings in dart:io. Now completely warning free.

sdk/lib/io/timer_impl.dart

Index: sdk/lib/io/timer_impl.dart
diff --git a/sdk/lib/io/timer_impl.dart b/sdk/lib/io/timer_impl.dart
index c08f3bb1c62b10f5b27e6800ee5f4ad86453daf2..cf92388ccd92bcf80f70119f2a497adf7184ed1f 100644
--- a/sdk/lib/io/timer_impl.dart
+++ b/sdk/lib/io/timer_impl.dart
@@ -84,7 +84,7 @@ class _Timer implements Timer {
         }
         entry = entry.nextEntry();
       }
-      _timers.addLast(this);
+      _timers.add(this);
     }
   }
 
@@ -132,7 +132,7 @@ class _Timer implements Timer {
         _Timer timer = entry.element;
         if (timer._wakeupTime <= currentTime) {
           entry.remove();
-          pending_timers.addLast(timer);
+          pending_timers.add(timer);
           entry = _timers.firstEntry();
         } else {
           break;