servo: Merge #8661 - Webdriver - GetWindowSize/IsEnabled/IsSelected (from craftytrickster:8623/some-webdriver-commands); r=jgraham

Added handlers for https://github.com/servo/servo/issues/8623:
GetWindowSize
IsEnabled(WebElement)
IsSelected(WebElement)

I am not sure how to actually verify my webdriver code works, if someone can give advice I would make the necessary changes.

Thanks!

Source-Repo: https://github.com/servo/servo
Source-Revision: a877a56e0e603c6cc8e9f951c2ad14b6fe8f9b62

servo/components/msg/webdriver_msg.rs

@@ -2,7 +2,7 @@
  * License, v. 2.0. If a copy of the MPL was not distributed with this
  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
 
-use constellation_msg::PipelineId;
+use constellation_msg::{PipelineId, WindowSizeData};
 use ipc_channel::ipc::IpcSender;
 use rustc_serialize::json::{Json, ToJson};
 use url::Url;
@@ -21,6 +21,9 @@ pub enum WebDriverScriptCommand {
     GetElementText(String, IpcSender<Result<String, ()>>),
     GetFrameId(WebDriverFrameId, IpcSender<Result<Option<PipelineId>, ()>>),
     GetUrl(IpcSender<Url>),
+    GetWindowSize(IpcSender<Option<WindowSizeData>>),
+    IsEnabled(String, IpcSender<Result<bool, ()>>),
+    IsSelected(String, IpcSender<Result<bool, ()>>),
     GetTitle(IpcSender<String>)
 }