Auto merge of #24859 - jdm:surfman-fallible, r=Manishearth

Don't panic if surfman initialization fails.

Since WebGL is only one component of the web platform, there's no reason that failing to initialize surfman for webgl support should take down the entire browser.

---
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] These changes fix #24642 (in that the browser will now start up) and fix #24627
- [x] These changes do not require tests because tests for graphics acceleration? don't make me laugh.

components/servo/lib.rs

@@ -511,7 +511,7 @@ where
             webrender_api_sender,
             webxr_main_thread.registry(),
             player_context,
-            Some(webgl_threads),
+            webgl_threads,
             webvr_chan,
             webvr_constellation_sender,
             glplayer_threads,
@@ -1027,7 +1027,7 @@ fn create_webgl_threads<W>(
     webxr_main_thread: &mut webxr::MainThreadRegistry,
     external_image_handlers: &mut WebrenderExternalImageHandlers,
     external_images: Arc<Mutex<WebrenderExternalImageRegistry>>,
-) -> WebGLThreads
+) -> Option<WebGLThreads>
 where
     W: WindowMethods + 'static + ?Sized,
 {
@@ -1037,18 +1037,33 @@ where
     #[cfg(not(target_os = "windows"))]
     let (device, context) = unsafe {
         if opts::get().headless {
-            let (device, context) = SWDevice::from_current_context()
+            let (device, context) = match SWDevice::from_current_context() {
-                .expect("Failed to create software graphics context!");
+                Ok(a) => a,
+                Err(e) => {
+                    warn!("Failed to create software graphics context: {:?}", e);
+                    return None;
+                },
+            };
             (Device::Software(device), Context::Software(context))
         } else {
-            let (device, context) = HWDevice::from_current_context()
+            let (device, context) = match HWDevice::from_current_context() {
-                .expect("Failed to create hardware graphics context!");
+                Ok(a) => a,
+                Err(e) => {
+                    warn!("Failed to create hardware graphics context: {:?}", e);
+                    return None;
+                },
+            };
             (Device::Hardware(device), Context::Hardware(context))
         }
     };
     #[cfg(target_os = "windows")]
-    let (device, context) =
+    let (device, context) = match unsafe { Device::from_current_context() } {
-        unsafe { Device::from_current_context().expect("Failed to create graphics context!") };
+        Ok(a) => a,
+        Err(e) => {
+            warn!("Failed to create graphics context: {:?}", e);
+            return None;
+        },
+    };
 
     let gl_type = match window.gl().get_type() {
         gleam::gl::GlType::Gl => sparkle::gl::GlType::Gl,
@@ -1081,5 +1096,5 @@ where
         webrender.set_output_image_handler(output_handler);
     }
 
-    webgl_threads
+    Some(webgl_threads)
 }