Spurious scrollbars should not be drawn when overflow is applied to a frame.

It doesn't really make sense to get overflow scrollbars for an iframe (the real scrollbars are drawn within the frame, and the frame itself cannot overflow in any useful way). Rather than address this in the legacy compositing code, this makes the style system prevent this nonsensical state from ever occurring, by adjusting the overflow property to visible for all frame elements. This matches the existing behavior of the non-composited path here: no scrollbars are drawn in response to the 'overflow' property on a frame. BUG=384154 TEST=LayoutTests/scrollbars/iframe-overflow-scroll-ignored.html Review URL: https://codereview.chromium.org/1843723002 Cr-Commit-Position: refs/heads/master@{#383855}

Spurious scrollbars should not be drawn when overflow is applied to a frame.
It doesn't really make sense to get overflow scrollbars for an iframe (the real scrollbars are drawn within the frame, and the frame itself cannot overflow in any useful way). Rather than address this in the legacy compositing code, this makes the style system prevent this nonsensical state from ever occurring, by adjusting the overflow property to visible for all frame elements. This matches the existing behavior of the non-composited path here: no scrollbars are drawn in response to the 'overflow' property on a frame. BUG=384154 TEST=LayoutTests/scrollbars/iframe-overflow-scroll-ignored.html Review URL: https://codereview.chromium.org/1843723002 Cr-Commit-Position: refs/heads/master@{#383855}
55de872c · jbroman · Commit bot · d7b5be44 · 55de872c · 55de872c
Commit 55de872c authored Mar 29, 2016 by jbroman Committed by Commit bot Mar 29, 2016
3 changed files
--- a/third_party/WebKit/LayoutTests/scrollbars/iframe-overflow-scroll-ignored-expected.html
+++ b/third_party/WebKit/LayoutTests/scrollbars/iframe-overflow-scroll-ignored-expected.html
+<!DOCTYPE html>
+<iframe srcdoc="<div style=height:1000px></div>"></iframe>
--- a/third_party/WebKit/LayoutTests/scrollbars/iframe-overflow-scroll-ignored.html
+++ b/third_party/WebKit/LayoutTests/scrollbars/iframe-overflow-scroll-ignored.html
+<!DOCTYPE html>
+<!-- There should be a functioning vertical scrollbar, but no horizontal scrollbar. -->
+<iframe style="overflow-x: scroll; overflow-y: hidden" srcdoc="<div style=height:1000px></div>"></iframe>
--- a/third_party/WebKit/Source/core/css/resolver/StyleAdjuster.cpp
+++ b/third_party/WebKit/Source/core/css/resolver/StyleAdjuster.cpp
@@ -349,6 +349,14 @@ void StyleAdjuster::adjustStyleForHTMLElement(ComputedStyle& style, const Comput
        return;
    }

+    if (isHTMLFrameElementBase(element)) {
+        // Frames cannot overflow (they are always the size we ask them to be).
+        // Some compositing code paths may try to draw scrollbars anyhow.
+        style.setOverflowX(OverflowVisible);
+        style.setOverflowY(OverflowVisible);
+        return;
+    }
+
    if (isHTMLRTElement(element)) {
        // Ruby text does not support float or position. This might change with evolution of the specification.
        style.setPosition(StaticPosition);