Java client side support for launch_app command of chromedriver:

/session/$sessionId/chromium/launch_app
This is using the approach proposed by @richardrb
in pull request #168

java/client/src/org/openqa/selenium/chrome/ChromeDriver.java

@@ -18,6 +18,7 @@
 
 package org.openqa.selenium.chrome;
 
+import com.google.common.collect.ImmutableMap;
 import org.openqa.selenium.Capabilities;
 import org.openqa.selenium.WebDriver;
 import org.openqa.selenium.WebDriverException;
@@ -30,7 +31,6 @@
 import org.openqa.selenium.remote.RemoteWebDriver;
 import org.openqa.selenium.remote.html5.RemoteLocationContext;
 import org.openqa.selenium.remote.html5.RemoteWebStorage;
-import org.openqa.selenium.remote.service.DriverCommandExecutor;
 
 /**
  * A {@link WebDriver} implementation that controls a Chrome browser running on the local machine.
@@ -167,7 +167,7 @@ public ChromeDriver(ChromeDriverService service, ChromeOptions options) {
    * @param capabilities The capabilities required from the ChromeDriver.
    */
   public ChromeDriver(ChromeDriverService service, Capabilities capabilities) {
-    super(new DriverCommandExecutor(service), capabilities);
+    super(new ChromeDriverCommandExecutor(service), capabilities);
     locationContext = new RemoteLocationContext(getExecuteMethod());
     webStorage = new  RemoteWebStorage(getExecuteMethod());
   }
@@ -198,4 +198,11 @@ public Location location() {
   public void setLocation(Location location) {
     locationContext.setLocation(location);
   }
+
+  /**
+   * Launches Chome app specified by id.
+   */
+  public void launchApp(String id) {
+    execute(ChromeDriverCommand.LAUNCH_APP, ImmutableMap.of("id", id));
+  }
 }

java/client/src/org/openqa/selenium/chrome/ChromeDriverCommand.java

@@ -0,0 +1,27 @@
+// Licensed to the Software Freedom Conservancy (SFC) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The SFC licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package org.openqa.selenium.chrome;
+
+/**
+ * Constants for the ChromeDriver specific command IDs.
+ */
+final class ChromeDriverCommand {
+  private ChromeDriverCommand() {}
+
+  static final String LAUNCH_APP = "launchApp";
+}

java/client/src/org/openqa/selenium/chrome/ChromeDriverCommandExecutor.java

@@ -0,0 +1,42 @@
+// Licensed to the Software Freedom Conservancy (SFC) under one
+// or more contributor license agreements.  See the NOTICE file
+// distributed with this work for additional information
+// regarding copyright ownership.  The SFC licenses this file
+// to you under the Apache License, Version 2.0 (the
+// "License"); you may not use this file except in compliance
+// with the License.  You may obtain a copy of the License at
+//
+//   http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing,
+// software distributed under the License is distributed on an
+// "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+// KIND, either express or implied.  See the License for the
+// specific language governing permissions and limitations
+// under the License.
+
+package org.openqa.selenium.chrome;
+
+import com.google.common.collect.ImmutableMap;
+
+import org.openqa.selenium.remote.CommandInfo;
+import org.openqa.selenium.remote.http.HttpMethod;
+
+import org.openqa.selenium.remote.service.DriverCommandExecutor;
+import org.openqa.selenium.remote.service.DriverService;
+
+import java.util.Map;
+
+/**
+ * {@link DriverCommandExecutor} that understands ChromeDriver specific commands.
+ */
+class ChromeDriverCommandExecutor extends DriverCommandExecutor {
+
+  private static final Map<String, CommandInfo> CHROME_COMMAND_NAME_TO_URL = ImmutableMap.of(
+      ChromeDriverCommand.LAUNCH_APP,
+      new CommandInfo("/session/:sessionId/chromium/launch_app", HttpMethod.POST));
+
+  public ChromeDriverCommandExecutor(DriverService service) {
+    super(service, CHROME_COMMAND_NAME_TO_URL);
+  }
+}