Revert "auto merge of #1356 : ksh8281/servo/remove_@_in_LayoutTask.FontContext, r=pcwalton"

This reverts commit e8ffac13d7, reversing
changes made to db923feffe.

Reverting this change because FreeType is *not* thread safe. See the
documentation here:

http://www.freetype.org/freetype2/docs/reference/ft2-base_interface.html

"In multi-threaded applications, make sure that the same FT_Library
object or any of its children doesn't get accessed in parallel."

We will need to use a `MutexArc` instead.

src/components/main/layout/layout_task.rs

@@ -77,6 +77,9 @@ struct LayoutTask {
     /// The local image cache.
     local_image_cache: MutexArc<LocalImageCache>,
 
+    /// The local font context.
+    font_ctx: @mut FontContext,
+
     /// The size of the viewport.
     screen_size: Option<Size2D<Au>>,
 
@@ -87,8 +90,6 @@ struct LayoutTask {
 
     /// The channel on which messages can be sent to the profiler.
     profiler_chan: ProfilerChan,
-
-    opts: Opts
 }
 
 /// The damage computation traversal.
@@ -228,6 +229,7 @@ impl LayoutTask {
            opts: &Opts,
            profiler_chan: ProfilerChan)
            -> LayoutTask {
+        let fctx = @mut FontContext::new(opts.render_backend, true, profiler_chan.clone());
 
         LayoutTask {
             id: id,
@@ -237,13 +239,13 @@ impl LayoutTask {
             render_chan: render_chan,
             image_cache_task: image_cache_task.clone(),
             local_image_cache: MutexArc::new(LocalImageCache(image_cache_task)),
+            font_ctx: fctx,
             screen_size: None,
 
             display_list: None,
 
             stylist: RWArc::new(new_stylist()),
             profiler_chan: profiler_chan,
-            opts: opts.clone()
         }
     }
 
@@ -257,8 +259,7 @@ impl LayoutTask {
     // Create a layout context for use in building display lists, hit testing, &c.
     fn build_layout_context(&self) -> LayoutContext {
         let image_cache = self.local_image_cache.clone();
-        let font_ctx = ~FontContext::new(self.opts.render_backend, true,
-                                            self.profiler_chan.clone());
+        let font_ctx = self.font_ctx;
         let screen_size = self.screen_size.unwrap();
 
         LayoutContext {
@@ -343,9 +344,9 @@ impl LayoutTask {
     /// is intertwined with selector matching, making it difficult to compare directly. It is
     /// marked `#[inline(never)]` to aid benchmarking in sampling profilers.
     #[inline(never)]
-    fn construct_flow_tree(&self, layout_context: &mut LayoutContext, node: AbstractNode<LayoutView>)
+    fn construct_flow_tree(&self, layout_context: &LayoutContext, node: AbstractNode<LayoutView>)
                            -> ~Flow: {
-        node.traverse_postorder_mut(&mut FlowConstructor::init(layout_context));
+        node.traverse_postorder(&FlowConstructor::init(layout_context));
 
         let result = match *node.mutate_layout_data().ptr {
             Some(ref mut layout_data) => {
@@ -440,7 +441,7 @@ impl LayoutTask {
         // Construct the flow tree.
         let mut layout_root = profile(time::LayoutTreeBuilderCategory,
                                       self.profiler_chan.clone(),
-                                      || self.construct_flow_tree(&mut layout_ctx, *node));
+                                      || self.construct_flow_tree(&layout_ctx, *node));
 
         // Propagate damage.
         layout_root.traverse_preorder(&mut PropagateDamageTraversal {