Implement ability to load driver providers using ServiceLoader. A use…

…r can add new providers or override existing ones. To use this ability a user should:

1) Create one or several classes that implement DriverProvider interface and have no-args constructor. The method getProvidedCapabilities should return capabilities to match against. The method newInstance should implement custom driver creation logic.
2) Create a file META-INF/services/org.openqa.selenium.remote.server.DriverProvider
and list your classes in this file (one full class name per line).
3) Start selenium server (or a node grid) with the classpath that includes your custom classes and META-INF directory that lists them.
4) Starting a node set -browser option with the parameters that correspont the capabilities returned by getProvidedCapabilities method of a provider.
Also I'm going to add a wiki page that describes this new feature in more details.

java/server/src/org/openqa/selenium/remote/server/DefaultDriverFactory.java

@@ -30,8 +30,11 @@ public class DefaultDriverFactory implements DriverFactory {
       new ConcurrentHashMap<Capabilities, DriverProvider>();
 
   public void registerDriver(Capabilities capabilities, Class<? extends WebDriver> implementation) {
-    capabilitiesToDriverProvider.put(capabilities,
-                                     new DefaultDriverProvider(capabilities, implementation));
+    registerDriverProvider(capabilities, new DefaultDriverProvider(capabilities, implementation));
+  }
+
+  public void registerDriverProvider(Capabilities capabilities, DriverProvider implementation) {
+    capabilitiesToDriverProvider.put(capabilities, implementation);
   }
 
   protected Class<? extends WebDriver> getBestMatchFor(Capabilities desired) {

java/server/src/org/openqa/selenium/remote/server/DefaultDriverSessions.java

@@ -25,6 +25,7 @@
 import java.util.Collections;
 import java.util.HashMap;
 import java.util.Map;
+import java.util.ServiceLoader;
 import java.util.Set;
 import java.util.UUID;
 import java.util.concurrent.ConcurrentHashMap;
@@ -65,6 +66,7 @@ public DefaultDriverSessions(
   protected DefaultDriverSessions(Platform runningOn, DriverFactory factory) {
     this.factory = factory;
     registerDefaults(runningOn);
+    registerDriverProviders(runningOn);
   }
 
   private void registerDefaults(Platform current) {
@@ -81,6 +83,18 @@ private void registerDefaults(Platform current) {
     }
   }
 
+  private void registerDriverProviders(Platform current) {
+    for (DriverProvider provider : ServiceLoader.load(DriverProvider.class)) {
+      Capabilities caps = provider.getProvidedCapabilities();
+      if (caps.getPlatform() == null || caps.getPlatform().is(current)) {
+        factory.registerDriverProvider(caps, provider);
+      } else {
+        log.info("Driver provider " + provider + " registration is skipped: registration capabilities "
+                 + caps.toString() + " does not match with current platform: " + current.toString());
+      }
+    }
+  }
+
   private void registerDriver(Capabilities caps, String className) {
     try {
       registerDriver(caps, Class.forName(className).asSubclass(WebDriver.class));

java/server/src/org/openqa/selenium/remote/server/DriverFactory.java

@@ -21,6 +21,8 @@
 public interface DriverFactory {
   void registerDriver(Capabilities capabilities, Class<? extends WebDriver> implementation);
 
+  void registerDriverProvider(Capabilities capabilities, DriverProvider implementation);
+
   WebDriver newInstance(Capabilities capabilities);
 
   boolean hasMappingFor(Capabilities capabilities);