Add a permission to shell for running multi window tests.

Bug: 19225708
Change-Id: Ia2de679b133acee992ccdab3bfddbdd9d78f5025
diff --git a/packages/Shell/AndroidManifest.xml b/packages/Shell/AndroidManifest.xml
index 1c4c012..c6d9e98 100644
--- a/packages/Shell/AndroidManifest.xml
+++ b/packages/Shell/AndroidManifest.xml
@@ -108,6 +108,7 @@
     <uses-permission android:name="android.permission.REGISTER_SIM_SUBSCRIPTION" />
     <uses-permission android:name="android.permission.GET_APP_OPS_STATS" />
     <uses-permission android:name="android.permission.VIBRATE" />
+    <uses-permission android:name="android.permission.MANAGE_ACTIVITY_STACKS" />
 
     <application android:label="@string/app_label"
                  android:forceDeviceEncrypted="true"