Launch activity behind launching task.

Use ActivityOptions.makeLaunchTaskBehindAnimation() to launch tasks
behind the current task. Includes animations for launching and
launched tasks.

Fixes bug 16157517.

Change-Id: I0a94af70b4748592e94673b958ee824cfb3d7ec0
diff --git a/services/core/java/com/android/server/wm/AppWindowToken.java b/services/core/java/com/android/server/wm/AppWindowToken.java
index 12c15e2..312689b 100644
--- a/services/core/java/com/android/server/wm/AppWindowToken.java
+++ b/services/core/java/com/android/server/wm/AppWindowToken.java
@@ -109,6 +109,8 @@
 
     boolean mDeferRemoval;
 
+    boolean mLaunchTaskBehind;
+
     AppWindowToken(WindowManagerService _service, IApplicationToken _token,
             boolean _voiceInteraction) {
         super(_service, _token.asBinder(),