Auto merge of #16807 - mrobinson:scroll-clamping, r=emilio

Fix clamping of scroll position in window.scrollBy

For rightward and downward overflow the spec says:

Let x be max(0, min(x, viewport scrolling area width - viewport width)).
Let y be max(0, min(y, viewport scrolling area height - viewport height)).

Previously, those operations were reversed, which created negative
overflow even when the overflow direction was downward. This change
ensures that Servo matches spec behavior.

<!-- Please describe your changes on the following line: -->

---
<!-- Thank you for contributing to Servo! Please replace each `[ ]` by `[X]` when the step is complete, and replace `__` with appropriate data: -->
- [x] `./mach build -d` does not report any errors
- [x] `./mach test-tidy` does not report any errors
- [ ] These changes fix #__ (github issue number if applicable).

<!-- Either: -->
- [x] There are tests for these changes OR
- [ ] These changes do not require tests because _____

<!-- Also, please make sure that "Allow edits from maintainers" checkbox is checked, so that we can help you if you get stuck somewhere along the way.-->

<!-- Pull requests that do not address these steps are welcome, but they will require additional verification as part of the review process. -->

<!-- Reviewable:start -->
---
This change is [<img src="https://reviewable.io/review_button.svg" height="34" align="absmiddle" alt="Reviewable"/>](https://reviewable.io/reviews/servo/servo/16807)
<!-- Reviewable:end -->

components/script/dom/window.rs

@@ -1066,8 +1066,8 @@ impl Window {
                 let content_size = e.upcast::<Node>().bounding_content_box_or_zero();
                 let content_height = content_size.size.height.to_f64_px();
                 let content_width = content_size.size.width.to_f64_px();
-                (xfinite.max(0.0f64).min(content_width - width),
-                 yfinite.max(0.0f64).min(content_height - height))
+                (xfinite.min(content_width - width).max(0.0f64),
+                 yfinite.min(content_height - height).max(0.0f64))
             },
             None => {
                 (xfinite.max(0.0f64), yfinite.max(0.0f64))