Auto merge of #24677 - jdm:iframe-sizing-cleanup, r=asajeffrey

Ensure all iframes are sized correctly at creation

Following in the path of #22395, these commits serve several purposes:
* prevent layout instability early during iframe loads caused by a succession of resize events
* reduce the complexity of determining what actual DPI and initial window size values are being used at startup
* ensure that all documents have a correct initial viewport size at creation

These changes fix problems that were exposed by the changes in #24462 but are independent of that PR.

---
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [x] There are tests for these changes

1 files changed, 10 insertions, 0 deletions

diff --git a/components/script/script_thread.rs b/components/script/script_thread.rs
index 6a7a69651e7..191df335ec5 100644
--- a/components/script/script_thread.rs
+++ b/components/script/script_thread.rs
@@ -2392,6 +2392,7 @@ impl ScriptThread {
                 load_data.url.clone(),
             ),
             layout_is_busy: layout_is_busy.clone(),
+            window_size,
         });
 
         // Pick a layout thread, any layout thread
@@ -3696,6 +3697,15 @@ impl ScriptThread {
         };
 
         let window = document.window();
+        if window.window_size() == new_size {
+            return;
+        }
+        debug!(
+            "resizing pipeline {:?} from {:?} to {:?}",
+            pipeline_id,
+            window.window_size(),
+            new_size
+        );
         window.set_window_size(new_size);
         window.force_reflow(ReflowGoal::Full, ReflowReason::WindowResize);