Disable the backup feature entirely.

Downgrading to targetSdkVersion 22 broke the Play Store upgrade process,
so this is my only remaining option.

app/build.gradle

@@ -7,10 +7,7 @@ android {
     defaultConfig {
         applicationId 'net.pmarks.chromadoze'
         minSdkVersion 8
-        // Not using targetSdkVersion >= 23, because Android 6.0 has a bug which
-        // effectively runs "bmgr fullbackup net.pmarks.chromadoze" in the middle of
-        // the night, killing the foreground service.
-        targetSdkVersion 22
+        targetSdkVersion 23
     }
 
     buildTypes {

app/src/main/AndroidManifest.xml

@@ -1,14 +1,18 @@
 <?xml version="1.0" encoding="utf-8"?>
 <manifest xmlns:android="http://schemas.android.com/apk/res/android"
     package="net.pmarks.chromadoze"
-    android:versionCode="20"
-    android:versionName="3.5.3">
+    android:versionCode="21"
+    android:versionName="3.5.4">
 
     <uses-permission android:name="android.permission.WAKE_LOCK" />
 
+    <!-- Note: When allowBackup is enabled, Android 6.0 will randomly kill the
+         service after a few hours.  The alternative is to stay on
+         targetSdkVersion 22, but the upgrade/downgrade caused the Play store
+         to fail with (Error code: -504),  So my hands are tied, and disabling
+         backup is the only solution I can find. -->
     <application
-        android:allowBackup="true"
-        android:backupAgent="TheBackupAgent"
+        android:allowBackup="false"
         android:icon="@drawable/chromadoze_icon"
         android:label="@string/app_name"
         android:theme="@style/Theme.ChromaDozeTheme">
@@ -29,8 +33,5 @@
         </receiver>
 
         <service android:name=".NoiseService" />
-        <meta-data
-            android:name="com.google.android.backup.api_key"
-            android:value="AEdPqrEAAAAISXaOEWnqsGHIpO7oONbmE9wULxVx_vswtaPpGA" />
     </application>
 </manifest>

app/src/main/java/net/pmarks/chromadoze/ChromaDoze.java

@@ -17,7 +17,6 @@
 
 package net.pmarks.chromadoze;
 
-import android.app.backup.BackupManager;
 import android.content.SharedPreferences;
 import android.graphics.Bitmap;
 import android.graphics.PorterDuff.Mode;
@@ -129,7 +128,6 @@ protected void onPause() {
         pref.clear();
         mUiState.saveState(pref);
         pref.commit();
-        new BackupManager(this).dataChanged();
 
         // Stop receiving progress events.
         NoiseService.removePercentListener(this);