Allow subclasses of HttpCommandExecutor to extend it at runtime.

This is useful for projects such as Selendroid, which currently
have to jump through some ugly hoops in order to do this.

Author: shs96c

java/client/src/org/openqa/selenium/remote/HttpCommandExecutor.java

@@ -21,6 +21,7 @@
 import static org.openqa.selenium.remote.DriverCommand.NEW_SESSION;
 import static org.openqa.selenium.remote.DriverCommand.QUIT;
 
+import com.google.common.base.Preconditions;
 import com.google.common.base.Throwables;
 import com.google.common.collect.ImmutableMap;
 
@@ -116,11 +117,23 @@ public HttpCommandExecutor(Map<String, CommandInfo> additionalCommands, URL addr
         host, remoteServer.getPort(), remoteServer.getProtocol());
 
     for (Map.Entry<String, CommandInfo> entry : additionalCommands.entrySet()) {
-      CommandInfo info = entry.getValue();
-      commandCodec.defineCommand(entry.getKey(), info.getMethod(), info.getUrl());
+      defineCommand(entry.getKey(), entry.getValue());
     }
   }
 
+  /**
+   * It may be useful to extend the commands understood by this {@code HttpCommandExecutor} at run
+   * time, and this can be achieved via this method. Note, this is protected, and expected usage is
+   * for subclasses only to call this.
+   *
+   * @param commandName The name of the command to use.
+   */
+  protected void defineCommand(String commandName, CommandInfo info) {
+    Preconditions.checkNotNull(commandName);
+    Preconditions.checkNotNull(info);
+    commandCodec.defineCommand(commandName, info.getMethod(), info.getUrl());
+  }
+
   public void setLocalLogs(LocalLogs logs) {
     this.logs = logs;
   }