Use a global static variable for IdNamespace counting.

Author: JerryShih

webrender/src/render_backend.rs

@@ -124,6 +124,10 @@ enum DocumentOp {
     Rendered(RendererFrame),
 }
 
+/// The unique id for WR resource identification. This id is not thread safe.
+/// The RenderBackend should be created in the same thread.
+static mut NEXT_NAMESPACE_ID: IdNamespace = IdNamespace(1);
+
 /// The render backend is responsible for transforming high level display lists into
 /// GPU-friendly work which is then submitted to the renderer in the form of a frame::Frame.
 ///
@@ -133,7 +137,6 @@ pub struct RenderBackend {
     payload_rx: PayloadReceiver,
     payload_tx: PayloadSender,
     result_tx: Sender<ResultMsg>,
-    next_namespace_id: IdNamespace,
     default_device_pixel_ratio: f32,
 
     gpu_cache: GpuCache,
@@ -177,7 +180,6 @@ impl RenderBackend {
             gpu_cache: GpuCache::new(),
             frame_config,
             documents: FastHashMap::default(),
-            next_namespace_id: IdNamespace(1),
             notifier,
             recorder,
 
@@ -452,9 +454,11 @@ impl RenderBackend {
                     tx.send(glyph_indices).unwrap();
                 }
                 ApiMsg::CloneApi(sender) => {
-                    let namespace = self.next_namespace_id;
-                    self.next_namespace_id = IdNamespace(namespace.0 + 1);
-                    sender.send(namespace).unwrap();
+                    unsafe {
+                        let namespace = NEXT_NAMESPACE_ID;
+                        NEXT_NAMESPACE_ID = IdNamespace(NEXT_NAMESPACE_ID.0 + 1);
+                        sender.send(namespace).unwrap();
+                    }
                 }
                 ApiMsg::AddDocument(document_id, initial_size) => {
                     let document = Document::new(