Implemented the 'Throw' operator with scheduler

Author: zsxwing

rxjava-core/src/main/java/rx/Observable.java

@@ -578,11 +578,30 @@ public static <T> Observable<T> empty(Scheduler scheduler) {
      * @param <T>
      *            the type of the items (ostensibly) emitted by the Observable
      * @return an Observable that invokes the {@link Observer}'s {@link Observer#onError onError} method when the Observer subscribes to it
+     * @see <a href="http://msdn.microsoft.com/en-us/library/hh244299(v=vs.103).aspx">MSDN: Observable.Throw Method</a>
      */
     public static <T> Observable<T> error(Throwable exception) {
         return new ThrowObservable<T>(exception);
     }
 
+    /**
+     * Returns an Observable that invokes an {@link Observer}'s {@link Observer#onError onError} method with the specified scheduler.
+     * <p>
+     * <img width="640" src="https://raw.github.com/wiki/Netflix/RxJava/images/rx-operators/error.png">
+     *
+     * @param exception
+     *            the particular error to report
+     * @param scheduler
+     *            the scheduler to call the {@link Observer#onError onError} method.
+     * @param <T>
+     *            the type of the items (ostensibly) emitted by the Observable
+     * @return an Observable that invokes the {@link Observer}'s {@link Observer#onError onError} method with the specified scheduler.
+     * @see <a href="http://msdn.microsoft.com/en-us/library/hh211711(v=vs.103).aspx">MSDN: Observable.Throw Method</a>
+     */
+    public static <T> Observable<T> error(Throwable exception, Scheduler scheduler) {
+        return Observable.<T> error(exception).observeOn(scheduler);
+    }
+
     /**
      * Converts an {@link Iterable} sequence into an Observable.
      * <p>