When moving past a left-hand scrollbar, don't jump way outside the content box.

third_party/WebKit/Source/core/layout/LayoutBox.cpp

Index: third_party/WebKit/Source/core/layout/LayoutBox.cpp
diff --git a/third_party/WebKit/Source/core/layout/LayoutBox.cpp b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
index 097fec971dac558f6d294e287ee84ef1491c2e7a..dd6cd31daa600628f52523a90625cb9166c21659 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
@@ -973,6 +973,17 @@ int LayoutBox::HorizontalScrollbarHeight() const {
   return GetScrollableArea()->HorizontalScrollbarHeight();
 }
 
+LayoutUnit LayoutBox::VerticalScrollbarWidthClampedToContentBox() const {
+  LayoutUnit width(VerticalScrollbarWidth());
+  DCHECK_GE(width, LayoutUnit());
+  if (width) {
+    LayoutUnit minimum_width = LogicalWidth() - BorderAndPaddingLogicalWidth();
+    DCHECK_GE(minimum_width, LayoutUnit());
+    width = std::min(width, minimum_width);
+  }
+  return width;
+}
+
 ScrollResult LayoutBox::Scroll(ScrollGranularity granularity,
                                const FloatSize& delta) {
   // Presumably the same issue as in setScrollTop. See crbug.com/343132.