Make WallpaperMS bind wallpaper component PendingIntent immutable.

Require that the PendingIntent be immutable so that a malicious app is
not able to hijack and mutate any of the details.

Fixes: 154915372
Test: build & flash, change wallpaper manually.
Change-Id: I59b48811b26736bf0575769107dd940ca33ccf8d
(cherry picked from commit d4bd69cef05d379555418a8fe748ec94ff6bd6d0)
diff --git a/services/core/java/com/android/server/wallpaper/WallpaperManagerService.java b/services/core/java/com/android/server/wallpaper/WallpaperManagerService.java
index f669187..1d634d3 100644
--- a/services/core/java/com/android/server/wallpaper/WallpaperManagerService.java
+++ b/services/core/java/com/android/server/wallpaper/WallpaperManagerService.java
@@ -2373,7 +2373,7 @@
                     mContext, 0,
                     Intent.createChooser(new Intent(Intent.ACTION_SET_WALLPAPER),
                             mContext.getText(com.android.internal.R.string.chooser_wallpaper)),
-                    0, null, new UserHandle(serviceUserId)));
+                    PendingIntent.FLAG_IMMUTABLE, null, new UserHandle(serviceUserId)));
             if (!mContext.bindServiceAsUser(intent, newConn,
                     Context.BIND_AUTO_CREATE | Context.BIND_SHOWING_UI
                             | Context.BIND_FOREGROUND_SERVICE_WHILE_AWAKE,