Ensure layout/script always have a correct viewport size when a new pipeline is created.

components/constellation/constellation.rs

@@ -2216,6 +2216,7 @@ where
             new_pipeline_id: new_pipeline_id,
             replace: None,
             new_browsing_context_info: None,
+            window_size,
         });
     }
 
@@ -2360,6 +2361,7 @@ where
                 is_private: is_private,
                 is_visible: is_visible,
             }),
+            window_size,
         });
     }
 
@@ -2531,6 +2533,10 @@ where
         // https://github.com/rust-lang/rust/issues/59159
         let browsing_context_size = browsing_context.size;
         let browsing_context_is_visible = browsing_context.is_visible;
+        debug_assert_eq!(
+            browsing_context_size,
+            load_info.window_size.initial_viewport
+        );
 
         // Create the new pipeline, attached to the parent and push to pending changes
         self.new_pipeline(
@@ -2552,6 +2558,7 @@ where
             replace: replace,
             // Browsing context for iframe already exists.
             new_browsing_context_info: None,
+            window_size: load_info.window_size.initial_viewport,
         });
     }
 
@@ -2610,6 +2617,7 @@ where
                 is_private: is_private,
                 is_visible: is_parent_visible,
             }),
+            window_size: load_info.window_size.initial_viewport,
         });
     }
 
@@ -2698,6 +2706,7 @@ where
                 is_private: is_opener_private,
                 is_visible: is_opener_visible,
             }),
+            window_size: self.window_size.initial_viewport,
         });
     }
 
@@ -2901,6 +2910,7 @@ where
                     replace,
                     // `load_url` is always invoked on an existing browsing context.
                     new_browsing_context_info: None,
+                    window_size,
                 });
                 Some(new_pipeline_id)
             },
@@ -3220,6 +3230,7 @@ where
                     replace: Some(NeedsToReload::Yes(pipeline_id, load_data)),
                     // Browsing context must exist at this point.
                     new_browsing_context_info: None,
+                    window_size,
                 });
                 return;
             },
@@ -3977,7 +3988,7 @@ where
                     change.top_level_browsing_context_id,
                     change.new_pipeline_id,
                     new_context_info.parent_pipeline_id,
-                    self.window_size.initial_viewport, //XXXjdm is this valid?
+                    change.window_size,
                     new_context_info.is_private,
                     new_context_info.is_visible,
                 );

components/constellation/session_history.rs

@@ -3,6 +3,7 @@
  * file, You can obtain one at https://mozilla.org/MPL/2.0/. */
 
 use crate::browsingcontext::NewBrowsingContextInfo;
+use euclid::Size2D;
 use msg::constellation_msg::{
     BrowsingContextId, HistoryStateId, PipelineId, TopLevelBrowsingContextId,
 };
@@ -10,6 +11,7 @@ use script_traits::LoadData;
 use servo_url::ServoUrl;
 use std::cmp::PartialEq;
 use std::{fmt, mem};
+use style_traits::CSSPixel;
 
 /// Represents the joint session history
 /// https://html.spec.whatwg.org/multipage/#joint-session-history
@@ -122,6 +124,9 @@ pub struct SessionHistoryChange {
     /// Holds data for not-yet constructed browsing contexts that are not
     /// easily available when they need to be constructed.
     pub new_browsing_context_info: Option<NewBrowsingContextInfo>,
+
+    /// The size of the viewport for the browsing context.
+    pub window_size: Size2D<f32, CSSPixel>,
 }
 
 /// Represents a pipeline or discarded pipeline in a history entry.