Merge pull request ReactiveX#537 from landonf/scala-do-operator

Add scala adapters for doOnEach operator.

language-adaptors/rxjava-scala/src/main/scala/rx/lang/scala/Observable.scala

@@ -1818,6 +1818,65 @@ trait Observable[+T]
     new WithFilter[T](p, asJavaObservable)
   }
 
+  /**
+   * Returns an Observable that applies the given function to each item emitted by an
+   * Observable.
+   *
+   * @param observer the observer
+   *
+   * @return an Observable with the side-effecting behavior applied.
+   */
+  def doOnEach(observer: Observer[T]): Observable[T] = {
+    Observable[T](asJavaObservable.doOnEach(observer.asJavaObserver))
+  }
+
+  /**
+   * Returns an Observable that applies the given function to each item emitted by an
+   * Observable.
+   *
+   * @param onNext this function will be called whenever the Observable emits an item
+   *
+   * @return an Observable with the side-effecting behavior applied.
+   */
+  def doOnEach(onNext: T => Unit): Observable[T] = {
+    Observable[T](asJavaObservable.doOnEach(
+      onNext
+    ))
+  }
+
+  /**
+   * Returns an Observable that applies the given function to each item emitted by an
+   * Observable.
+   *
+   * @param onNext this function will be called whenever the Observable emits an item
+   * @param onError this function will be called if an error occurs
+   *
+   * @return an Observable with the side-effecting behavior applied.
+   */
+  def doOnEach(onNext: T => Unit, onError: Throwable => Unit): Observable[T] = {
+    Observable[T](asJavaObservable.doOnEach(
+      onNext,
+      onError
+    ))
+  }
+
+  /**
+   * Returns an Observable that applies the given function to each item emitted by an
+   * Observable.
+   *
+   * @param onNext this function will be called whenever the Observable emits an item
+   * @param onError this function will be called if an error occurs
+   * @param onCompleted the action to invoke when the source Observable calls
+   *
+   * @return an Observable with the side-effecting behavior applied.
+   */
+  def doOnEach(onNext: T => Unit, onError: Throwable => Unit, onCompleted: () => Unit): Observable[T] = {
+    Observable[T](asJavaObservable.doOnEach(
+      onNext,
+      onError,
+      onCompleted
+    ))
+  }
 }
 
 /**