Fix broken viewport percentage length units after a viewport resize.

When a viewport is resized, the computed values for a style containing viewport percentage length units become stale. However, there's no way for those styles to be invalidated after a resize. As a solution, this commit invalidates the computed values cache after a resize has occurred, which is probably over-kill.

A better solution would probably be to track under what conditions computed values remain valid, and invalidate them as indicated.

components/layout/context.rs

@@ -41,6 +41,10 @@ fn create_or_get_local_context(shared_layout_context: &SharedLayoutContext) -> *
                 style_sharing_candidate_cache: StyleSharingCandidateCache::new(),
             };
             r.set(unsafe { boxed::into_raw(context) });
+        } else if shared_layout_context.screen_size_changed {
+            unsafe {
+                (*r.get()).applicable_declarations_cache.evict_all();
+            }
         }
 
         r.get()
@@ -54,6 +58,9 @@ pub struct SharedLayoutContext {
     /// The current screen size.
     pub screen_size: Size2D<Au>,
 
+    /// Screen sized changed?
+    pub screen_size_changed: bool,
+
     /// A channel up to the constellation.
     pub constellation_chan: ConstellationChan,
 

components/layout/css/matching.rs

@@ -153,6 +153,10 @@ impl ApplicableDeclarationsCache {
     fn insert(&mut self, declarations: Vec<DeclarationBlock>, style: Arc<ComputedValues>) {
         self.cache.insert(ApplicableDeclarationsCacheEntry::new(declarations), style)
     }
+
+    pub fn evict_all(&mut self) {
+        self.cache.evict_all();
+    }
 }
 
 /// An LRU cache of the last few nodes seen, so that we can aggressively try to reuse their styles.

components/layout/layout_task.rs

@@ -311,12 +311,14 @@ impl LayoutTask {
     // Create a layout context for use in building display lists, hit testing, &c.
     fn build_shared_layout_context(&self,
                                    rw_data: &LayoutTaskData,
+                                   screen_size_changed: bool,
                                    reflow_root: &LayoutNode,
                                    url: &Url)
                                    -> SharedLayoutContext {
         SharedLayoutContext {
             image_cache: rw_data.local_image_cache.clone(),
             screen_size: rw_data.screen_size.clone(),
+            screen_size_changed: screen_size_changed,
             constellation_chan: rw_data.constellation_chan.clone(),
             layout_chan: self.chan.clone(),
             font_cache_task: self.font_cache_task.clone(),
@@ -774,11 +776,6 @@ impl LayoutTask {
                                          Au::from_frac32_px(viewport_size.height.get()));
         rw_data.screen_size = current_screen_size;
 
-        // Create a layout context for use throughout the following passes.
-        let mut shared_layout_context = self.build_shared_layout_context(&*rw_data,
-                                                                         node,
-                                                                         &data.url);
-
         // Handle conditions where the entire flow tree is invalid.
         let screen_size_changed = current_screen_size != old_screen_size;
 
@@ -803,6 +800,12 @@ impl LayoutTask {
                 |mut flow| LayoutTask::reflow_all_nodes(&mut *flow));
         }
 
+        // Create a layout context for use throughout the following passes.
+        let mut shared_layout_context = self.build_shared_layout_context(&*rw_data,
+                                                                         screen_size_changed,
+                                                                         node,
+                                                                         &data.url);
+
         let mut layout_root = profile(TimeProfilerCategory::LayoutStyleRecalc,
                                       self.profiler_metadata(data),
                                       self.time_profiler_chan.clone(),