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

ports/glutin/app.rs

@@ -70,7 +70,7 @@ impl App {
         // Handle browser state.
         let browser = Browser::new(window.clone());
 
-        let mut servo = Servo::new(embedder, window.clone(), device_pixels_per_px);
+        let mut servo = Servo::new(embedder, window.clone());
         let browser_id = BrowserId::new();
         servo.handle_events(vec![WindowEvent::NewBrowser(get_default_url(), browser_id)]);
         servo.setup_logging();

ports/libsimpleservo/api/src/lib.rs

@@ -211,7 +211,7 @@ pub fn init(
         gl: gl.clone(),
     });
 
-    let servo = Servo::new(embedder_callbacks, window_callbacks.clone(), None);
+    let servo = Servo::new(embedder_callbacks, window_callbacks.clone());
 
     SERVO.with(|s| {
         let mut servo_glue = ServoGlue {