Issue 6265 - Create shared AdblockEngine instance in AdblockWebView in background

libadblockplus-android-webview/src/org/adblockplus/libadblockplus/android/webview/AdblockWebView.java

 /*
  * This file is part of Adblock Plus <https://adblockplus.org/>,
  * Copyright (C) 2006-present eyeo GmbH
  *
  * Adblock Plus is free software: you can redistribute it and/or modify
  * it under the terms of the GNU General Public License version 3 as
  * published by the Free Software Foundation.
  *
  * Adblock Plus is distributed in the hope that it will be useful,
  * but WITHOUT ANY WARRANTY; without even the implied warranty of
@@ skipping 229 matching lines @@
     {
       return;
     }
 
     final Runnable setRunnable = new Runnable()
     {
       @Override
       public void run()
       {
         AdblockWebView.this.provider = provider;
-        AdblockWebView.this.provider.retain(true); // asynchronously
+        if (AdblockWebView.this.provider != null)
+        {
+          AdblockWebView.this.provider.retain(true); // asynchronously
+        }
       }
     };
 
     if (this.provider != null)
     {
       // as adblockEngine can be busy with elemhide thread we need to use callback
       this.dispose(setRunnable);
     }
     else
     {
@@ skipping 813 matching lines @@
         w("elemHideThread set to null");
         elemHideThread = null;
       }
     }
   };
 
   private void initAbpLoading()
   {
     getSettings().setJavaScriptEnabled(true);
     buildInjectJs();
-    initProvider();
-  }
-
-  private void initProvider()
+    ensureProvider();
+  }
+
+  private void ensureProvider()
   {
     // if AdblockWebView works as drop-in replacement for WebView 'provider' is not set.
     // Thus AdblockWebView is using SingleInstanceEngineProvider instance
     if (provider == null)
     {
       setProvider(new SingleInstanceEngineProvider(
         getContext(), AdblockEngine.BASE_PATH_DIRECTORY, debugMode));
     }
   }
 
@@ skipping 327 matching lines @@
         w("Busy with elemhide selectors, delayed disposing scheduled");
         elemHideThread.setFinishedRunnable(disposeRunnable);
       }
       else
       {
         disposeRunnable.run();
       }
     }
   }
 }