Clean up the timer source in the isolate library to be less VM specific.

sdk/lib/_internal/compiler/implementation/lib/isolate_patch.dart

Index: sdk/lib/_internal/compiler/implementation/lib/isolate_patch.dart
===================================================================
--- sdk/lib/_internal/compiler/implementation/lib/isolate_patch.dart	(revision 15985)
+++ sdk/lib/_internal/compiler/implementation/lib/isolate_patch.dart	(working copy)
@@ -1285,6 +1285,22 @@
   }
 }
 
-Timer _timerFactory(int millis, void callback(Timer timer), bool repeating) =>
-  repeating ? new _Timer.repeating(millis, callback)
-            : new _Timer(millis, callback);
+patch class Timer {
+  patch factory Timer(int milliSeconds, void callback(Timer timer)) {
+    if (_window == null) {
+      throw new UnsupportedError("Timer interface not supported.");
+    }
+    return new _Timer(milliSeconds, callbacl);
+  }
+
+  /**
+   * Creates a new repeating timer. The [callback] is invoked every
+   * [milliSeconds] millisecond until cancelled.
+   */
+  patch factory Timer.repeating(int milliSeconds, void callback(Timer timer)) {
+    if (_window == null) {
+      throw new UnsupportedError("Timer interface not supported.");
+    }
+    return new _Timer.repeating(milliSeconds, callbacl);
+  }
+}