Avoid memory leak in the Shutdown confirmation dialog.

How to reproduce:
1) Lock the screen.
2) Open the Phone options menu by long pressing the power
   button.
3) Tap "Power off" to display the confirmation dialog.
4) Repeat step 2 and 3 a few times (without closing the
   confirmation dialog.

Each time the confirmation dialog is displayed, a new
instance is created. A stack of confirmation dialogs are
created on the screen.

This is fixed by making sure the previous dialog is
dismissed before launching a new dialog.

Change-Id: I6b6c61ccc56364b66eed3528019f761e75bbe268

Author: Mattias Petersson

core/java/com/android/internal/app/ShutdownThread.java

@@ -76,6 +76,8 @@ public final class ShutdownThread extends Thread {
     private PowerManager.WakeLock mCpuWakeLock;
     private PowerManager.WakeLock mScreenWakeLock;
     private Handler mHandler;
+
+    private static AlertDialog sConfirmDialog;
 
     private ShutdownThread() {
     }
@@ -108,7 +110,10 @@ public static void shutdown(final Context context, boolean confirm) {
 
         if (confirm) {
             final CloseDialogReceiver closer = new CloseDialogReceiver(context);
-            final AlertDialog dialog = new AlertDialog.Builder(context)
+            if (sConfirmDialog != null) {
+                sConfirmDialog.dismiss();
+            }
+            sConfirmDialog = new AlertDialog.Builder(context)
                     .setTitle(com.android.internal.R.string.power_off)
                     .setMessage(resourceId)
                     .setPositiveButton(com.android.internal.R.string.yes, new DialogInterface.OnClickListener() {
@@ -118,10 +123,10 @@ public void onClick(DialogInterface dialog, int which) {
                     })
                     .setNegativeButton(com.android.internal.R.string.no, null)
                     .create();
-            closer.dialog = dialog;
-            dialog.setOnDismissListener(closer);
-            dialog.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD_DIALOG);
-            dialog.show();
+            closer.dialog = sConfirmDialog;
+            sConfirmDialog.setOnDismissListener(closer);
+            sConfirmDialog.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD_DIALOG);
+            sConfirmDialog.show();
         } else {
             beginShutdownSequence(context);
         }