Responding to review comments.

components/constellation/constellation.rs

@@ -293,7 +293,7 @@ impl<'a> Iterator for FrameTreeIterator<'a> {
 
 struct WebDriverData {
     load_channel: Option<(PipelineId, IpcSender<webdriver_msg::LoadStatus>)>,
-    resize_channel: Option<IpcSender<Option<WindowSizeData>>>,
+    resize_channel: Option<IpcSender<WindowSizeData>>,
 }
 
 impl WebDriverData {
@@ -1713,7 +1713,7 @@ impl<LTF: LayoutThreadFactory, STF: ScriptThreadFactory> Constellation<LTF, STF>
         }
 
         if let Some(resize_channel) = self.webdriver.resize_channel.take() {
-            let _ = resize_channel.send(Some(new_size));
+            let _ = resize_channel.send(new_size);
         }
 
         self.window_size = new_size;

components/msg/constellation_msg.rs

@@ -193,7 +193,7 @@ pub enum WebDriverCommandMsg {
     Refresh(PipelineId, IpcSender<LoadStatus>),
     ScriptCommand(PipelineId, WebDriverScriptCommand),
     SendKeys(PipelineId, Vec<(Key, KeyModifiers, KeyState)>),
-    SetWindowSize(PipelineId, Size2D<u32>, IpcSender<Option<WindowSizeData>>),
+    SetWindowSize(PipelineId, Size2D<u32>, IpcSender<WindowSizeData>),
     TakeScreenshot(PipelineId, IpcSender<Option<Image>>),
 }
 

components/webdriver_server/lib.rs

@@ -223,7 +223,7 @@ impl Handler {
             constellation_chan: constellation_chan,
             script_timeout: 30_000,
             load_timeout: 300_000,
-            resize_timeout: 30_000,
+            resize_timeout: 500,
             implicit_wait_timeout: 0
         }
     }
@@ -379,19 +379,19 @@ impl Handler {
         self.constellation_chan.send(ConstellationMsg::WebDriverCommand(cmd_msg)).unwrap();
 
         let timeout = self.resize_timeout;
+        let constellation_chan = self.constellation_chan.clone();
         thread::spawn(move || {
+            // On timeout, we send a GetWindowSize message to the constellation,
+            // which will give the current window size.
             thread::sleep(Duration::from_millis(timeout as u64));
-            let _ = sender.send(None);
+            let cmd_msg = WebDriverCommandMsg::GetWindowSize(pipeline_id, sender);
+            constellation_chan.send(ConstellationMsg::WebDriverCommand(cmd_msg)).unwrap();
         });
 
-        match receiver.recv().unwrap() {
-            Some(window_size) => {
-                let vp = window_size.visible_viewport;
-                let window_size_response = WindowSizeResponse::new(vp.width.get() as u64, vp.height.get() as u64);
-                Ok(WebDriverResponse::WindowSize(window_size_response))
-            },
-            None => Err(WebDriverError::new(ErrorStatus::Timeout, "Resize timed out")),
-        }
+        let window_size = receiver.recv().unwrap();
+        let vp = window_size.visible_viewport;
+        let window_size_response = WindowSizeResponse::new(vp.width.get() as u64, vp.height.get() as u64);
+        Ok(WebDriverResponse::WindowSize(window_size_response))
     }
 
     fn handle_is_enabled(&self, element: &WebElement) -> WebDriverResult<WebDriverResponse> {