Add SystemBootstrap class to support custom implementation of loadLibrary.

Client can provide their own implementation that calls System.load with absolute
paths instead of using the default System.loadLibrary implementation.

Author: jjlauer

java/org/cef/CefApp.java

@@ -140,14 +140,14 @@ private CefApp(String[] args, CefSettings settings) throws UnsatisfiedLinkError
         super(args);
         if (settings != null) settings_ = settings.clone();
         if (OS.isWindows()) {
-            System.loadLibrary("jawt");
-            System.loadLibrary("chrome_elf");
-            System.loadLibrary("libcef");
+            SystemBootstrap.loadLibrary("jawt");
+            SystemBootstrap.loadLibrary("chrome_elf");
+            SystemBootstrap.loadLibrary("libcef");
 
             // Other platforms load this library in CefApp.startup().
-            System.loadLibrary("jcef");
+            SystemBootstrap.loadLibrary("jcef");
         } else if (OS.isLinux()) {
-            System.loadLibrary("cef");
+            SystemBootstrap.loadLibrary("cef");
         }
         if (appHandler_ == null) {
             appHandler_ = this;
@@ -520,7 +520,7 @@ public void actionPerformed(ActionEvent evt) {
      */
     public static final boolean startup() {
         if (OS.isLinux() || OS.isMacintosh()) {
-            System.loadLibrary("jcef");
+            SystemBootstrap.loadLibrary("jcef");
             return N_Startup();
         }
         return true;

java/org/cef/SystemBootstrap.java

@@ -0,0 +1,38 @@
+// Copyright (c) 2020 The Chromium Embedded Framework Authors. All rights
+// reserved. Use of this source code is governed by a BSD-style license that
+// can be found in the LICENSE file.
+package org.cef;
+
+/**
+ * To allow customization of System.load() calls by supplying a different
+ * implementation.  You'll want to call <code>setLoader</code> with your custom
+ * implementation before calling into any other CEF classes which then in turn
+ * will start triggering libraries to be loaded at runtime.
+ */
+public class SystemBootstrap {
+    /**
+     * Simple interface for how a library by name should be loaded.
+     */
+    static public interface Loader { public void loadLibrary(String libname); }
+
+    /**
+     * Default implementation is to call System.loadLibrary
+     */
+    static private Loader loader_ = new Loader() {
+        @Override
+        public void loadLibrary(String libname) {
+            System.loadLibrary(libname);
+        }
+    };
+
+    static public void setLoader(Loader loader) {
+        if (loader == null) {
+            throw new NullPointerException("Loader cannot be null");
+        }
+        loader_ = loader;
+    }
+
+    static public void loadLibrary(String libname) {
+        loader_.loadLibrary(libname);
+    }
+}