Allow Window implementations to indicate that they don't support a clipboard.

This is important for the SERVO_HEADLESS configuration, because
creating a clipboard on linux creates an X context which then causes
reftest instability.

components/compositing/constellation.rs

@@ -122,7 +122,7 @@ pub struct Constellation<LTF, STF> {
     pub window_size: WindowSizeData,
 
     /// Means of accessing the clipboard
-    clipboard_ctx: ClipboardContext,
+    clipboard_ctx: Option<ClipboardContext>,
 
     /// Bits of state used to interact with the webdriver implementation
     webdriver: WebDriverData
@@ -215,7 +215,8 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
                  time_profiler_chan: time::ProfilerChan,
                  mem_profiler_chan: mem::ProfilerChan,
                  devtools_chan: Option<DevtoolsControlChan>,
-                 storage_task: StorageTask)
+                 storage_task: StorageTask,
+                 supports_clipboard: bool)
                  -> ConstellationChan {
         let (constellation_port, constellation_chan) = ConstellationChan::new();
         let constellation_chan_clone = constellation_chan.clone();
@@ -248,7 +249,11 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
                     device_pixel_ratio: ScaleFactor::new(1.0),
                 },
                 phantom: PhantomData,
-                clipboard_ctx: ClipboardContext::new().unwrap(),
+                clipboard_ctx: if supports_clipboard {
+                    ClipboardContext::new().ok()
+                } else {
+                    None
+                },
                 webdriver: WebDriverData::new()
             };
             constellation.run();
@@ -438,13 +443,13 @@ impl<LTF: LayoutTaskFactory, STF: ScriptTaskFactory> Constellation<LTF, STF> {
                 self.handle_focus_msg(pipeline_id);
             }
             ConstellationMsg::GetClipboardContents(sender) => {
-                let result = match self.clipboard_ctx.get_contents() {
-                    Ok(s) => s,
-                    Err(e) => {
+                let result = self.clipboard_ctx.as_ref().map_or(
+                    "".to_string(),
+                    |ctx| ctx.get_contents().unwrap_or_else(|e| {
                         debug!("Error getting clipboard contents ({}), defaulting to empty string", e);
                         "".to_string()
-                    },
-                };
+                    })
+                );
                 sender.send(result).unwrap();
             }
             ConstellationMsg::WebDriverCommand(command) => {

components/compositing/windowing.rs

@@ -135,4 +135,7 @@ pub trait WindowMethods {
 
     /// Process a key event.
     fn handle_key(&self, key: Key, mods: KeyModifiers);
+
+    /// Does this window support a clipboard
+    fn supports_clipboard(&self) -> bool;
 }

components/servo/lib.rs

@@ -57,6 +57,7 @@ use profile_traits::mem;
 use profile_traits::time;
 use util::opts;
 
+use std::borrow::Borrow;
 use std::rc::Rc;
 use std::sync::mpsc::Sender;
 
@@ -91,6 +92,13 @@ impl Browser {
         // to deliver the message.
         let (compositor_proxy, compositor_receiver) =
             WindowMethods::create_compositor_channel(&window);
+        let supports_clipboard = match window {
+            Some(ref win_rc) => {
+                let win: &Window = win_rc.borrow();
+                win.supports_clipboard()
+            }
+            None => false
+        };
         let time_profiler_chan = profile_time::Profiler::create(opts.time_profiler_period);
         let mem_profiler_chan = profile_mem::Profiler::create(opts.mem_profiler_period);
         let devtools_chan = opts.devtools_port.map(|port| {
@@ -104,7 +112,8 @@ impl Browser {
                                                       compositor_proxy.clone_compositor_proxy(),
                                                       time_profiler_chan.clone(),
                                                       devtools_chan,
-                                                      mem_profiler_chan.clone());
+                                                      mem_profiler_chan.clone(),
+                                                      supports_clipboard);
 
         if let Some(port) = opts.webdriver_port {
             webdriver_server::start_server(port, constellation_chan.clone());
@@ -149,7 +158,8 @@ fn create_constellation(opts: opts::Opts,
                         compositor_proxy: Box<CompositorProxy+Send>,
                         time_profiler_chan: time::ProfilerChan,
                         devtools_chan: Option<Sender<devtools_traits::DevtoolsControlMsg>>,
-                        mem_profiler_chan: mem::ProfilerChan) -> ConstellationChan {
+                        mem_profiler_chan: mem::ProfilerChan,
+                        supports_clipboard: bool) -> ConstellationChan {
     let resource_task = new_resource_task(opts.user_agent.clone(), devtools_chan.clone());
 
     let image_cache_task = new_image_cache_task(resource_task.clone());
@@ -165,7 +175,8 @@ fn create_constellation(opts: opts::Opts,
         time_profiler_chan,
         mem_profiler_chan,
         devtools_chan,
-        storage_task);
+        storage_task,
+        supports_clipboard);
 
     // Send the URL command to the constellation.
     match opts.url {

ports/cef/window.rs

@@ -451,6 +451,10 @@ impl WindowMethods for Window {
             }
         }
     }
+
+    fn supports_clipboard(&self) -> bool {
+        true
+    }
 }
 
 struct CefCompositorProxy {

ports/glutin/window.rs

@@ -614,6 +614,10 @@ impl WindowMethods for Window {
             _ => {}
         }
     }
+
+    fn supports_clipboard(&self) -> bool {
+        true
+    }
 }
 
 /// The type of a window.
@@ -718,6 +722,10 @@ impl WindowMethods for Window {
     /// Helper function to handle keyboard events.
     fn handle_key(&self, _: Key, _: constellation_msg::KeyModifiers) {
     }
+
+    fn supports_clipboard(&self) -> bool {
+        false
+    }
 }
 
 struct GlutinCompositorProxy {

ports/gonk/src/window.rs

@@ -841,6 +841,10 @@ impl WindowMethods for Window {
     fn prepare_for_composite(&self, _width: usize, _height: usize) -> bool {
         true
     }
+
+    fn supports_clipboard(&self) -> bool {
+        true
+    }
 }
 
 struct GonkCompositorProxy {