Auto merge of #15913 - emilio:viewport-size, r=heycam,hiro

Use the proper viewport size for stylo

Reviewed upstream at [bug 1303229](https://bugzil.la/1303229).

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components/style/animation.rs

@@ -426,7 +426,7 @@ fn compute_style_for_animation_step(context: &SharedStyleContext,
             };
 
             let computed =
-                properties::apply_declarations(context.viewport_size,
+                properties::apply_declarations(context.viewport_size(),
                                                /* is_root = */ false,
                                                iter,
                                                previous_style,

components/style/context.rs

@@ -63,9 +63,6 @@ pub enum QuirksMode {
 /// There's exactly one of these during a given restyle traversal, and it's
 /// shared among the worker threads.
 pub struct SharedStyleContext {
-    /// The current viewport size.
-    pub viewport_size: Size2D<Au>,
-
     /// The CSS selector stylist.
     pub stylist: Arc<Stylist>,
 
@@ -93,6 +90,13 @@ pub struct SharedStyleContext {
     pub default_computed_values: Arc<ComputedValues>,
 }
 
+impl SharedStyleContext {
+    /// Return a suitable viewport size in order to be used for viewport units.
+    pub fn viewport_size(&self) -> Size2D<Au> {
+        self.stylist.device.au_viewport_size()
+    }
+}
+
 /// Information about the current element being processed. We group this together
 /// into a single struct within ThreadLocalStyleContext so that we can instantiate
 /// and destroy it easily at the beginning and end of element processing.

components/style/gecko/media_queries.rs

@@ -94,10 +94,10 @@ impl Device {
         self.viewport_override.as_ref().map(|v| {
             Size2D::new(Au::from_f32_px(v.size.width),
                         Au::from_f32_px(v.size.height))
-        }).unwrap_or_else(|| {
-            // TODO(emilio): Grab from pres context.
-            Size2D::new(Au::from_f32_px(1024.0),
-                        Au::from_f32_px(768.0))
+        }).unwrap_or_else(|| unsafe {
+            // TODO(emilio): Need to take into account scrollbars.
+            Size2D::new(Au((*self.pres_context).mVisibleArea.width),
+                        Au((*self.pres_context).mVisibleArea.height))
         })
     }
 }

components/style/gecko_bindings/bindings.rs

@@ -1373,8 +1373,7 @@ extern "C" {
                                            style: ServoComputedValuesBorrowed,
                                            parent_style:
                                                ServoComputedValuesBorrowedOrNull,
-                                           pres_context:
-                                               RawGeckoPresContextBorrowed,
+                                           set: RawServoStyleSetBorrowed,
                                            result:
                                                RawGeckoComputedKeyframeValuesListBorrowedMut);
 }

components/style/matching.rs

@@ -539,7 +539,7 @@ trait PrivateMatchMethods: TElement {
 
         // Invoke the cascade algorithm.
         let values =
-            Arc::new(cascade(shared_context.viewport_size,
+            Arc::new(cascade(shared_context.viewport_size(),
                              rule_node,
                              inherited_values,
                              layout_parent_style,