Recompute scroll origin when scrollbar existence has changed.

BUG=568706 R=eae@chromium.org Review URL: https://codereview.chromium.org/1553493003 Cr-Commit-Position: refs/heads/master@{#367185}

Recompute scroll origin when scrollbar existence has changed.
BUG=568706 R=eae@chromium.org Review URL: https://codereview.chromium.org/1553493003 Cr-Commit-Position: refs/heads/master@{#367185}
ed682d81 · szager · Commit bot · 428f9b85 · ed682d81 · ed682d81
Commit ed682d81 authored Dec 30, 2015 by szager Committed by Commit bot Dec 30, 2015
3 changed files
--- a/third_party/WebKit/LayoutTests/fast/scrolling/overflow-auto-ltr-expected.txt
+++ b/third_party/WebKit/LayoutTests/fast/scrolling/overflow-auto-ltr-expected.txt
+Check that the scroll offset in an LTR block is correctly preserved when the existence of its vertical scrollbar changes.
+
+On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
+
+
+PASS finalOffset is initialOffset
+PASS successfullyParsed is true
+
+TEST COMPLETE
+INNER INNER INNER
--- a/third_party/WebKit/LayoutTests/fast/scrolling/overflow-auto-ltr.html
+++ b/third_party/WebKit/LayoutTests/fast/scrolling/overflow-auto-ltr.html
+<!DOCTYPE html>
+<script src="../../resources/js-test.js"></script>
+<style>
+#scrollLeftRtl {
+  width: 100px;
+  height: 100px;
+  background-color: green;
+  direction: rtl;
+  overflow: scroll;
+}
+
+#inner {
+  white-space: nowrap;
+}
+</style>
+
+<div id="scrollLeftRtl">
+  <span id="inner">INNER INNER INNER</span>
+</div>
+
+<script>
+  description("Check that the scroll offset in an LTR block is correctly preserved when the existence of its vertical scrollbar changes.");
+
+  var scrollLeftDiv = document.getElementById("scrollLeftRtl");
+  var initialOffset = scrollLeftDiv.scrollWidth - scrollLeftDiv.clientWidth - scrollLeftDiv.scrollLeft;
+  scrollLeftDiv.style.overflow = "auto";
+  var finalOffset = scrollLeftDiv.scrollWidth - scrollLeftDiv.clientWidth - scrollLeftDiv.scrollLeft;
+  shouldBe("finalOffset", "initialOffset");
+</script>
--- a/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
+++ b/third_party/WebKit/Source/core/paint/PaintLayerScrollableArea.cpp
@@ -629,6 +629,9 @@ void PaintLayerScrollableArea::updateScrollDimensions(DoubleSize& scrollOffset,
            setHasVerticalScrollbar(hasVerticalOverflow);
        else if (box().style()->overflowY() == OSCROLL)
            setHasVerticalScrollbar(true);
+        // If vertical scrollbar existence has changed, LTR blocks need to update scroll origin to account
+        // for left-hand vertical scrollbar width.
+        computeScrollDimensions();
    }
 }