Make it possibe to lock the fixedLayoutSize

Source/core/platform/ScrollView.cpp

Index: Source/core/platform/ScrollView.cpp
diff --git a/Source/core/platform/ScrollView.cpp b/Source/core/platform/ScrollView.cpp
index 79dd29b7de9d91771665bda1a87fdbfa2f709ac0..405b588c521080a59346124d98c7cfcf6b2d6aaa 100644
--- a/Source/core/platform/ScrollView.cpp
+++ b/Source/core/platform/ScrollView.cpp
@@ -50,6 +50,7 @@ ScrollView::ScrollView()
     , m_updateScrollbarsPass(0)
     , m_drawPanScrollIcon(false)
     , m_useFixedLayout(false)
+    , m_fixedLayoutSizeLock(false)
     , m_paintsEntireContents(false)
     , m_clipsRepaints(true)
 {
@@ -205,13 +206,14 @@ IntSize ScrollView::unscaledVisibleContentSize(VisibleContentRectIncludesScrollb
 IntRect ScrollView::visibleContentRect(VisibleContentRectIncludesScrollbars scollbarInclusion) const
 {
     FloatSize visibleContentSize = unscaledVisibleContentSize(scollbarInclusion);
-    visibleContentSize.scale(1 / visibleContentScaleFactor());
+    if (!m_fixedLayoutSizeLock)
+        visibleContentSize.scale(1 / visibleContentScaleFactor());
     return IntRect(IntPoint(m_scrollOffset), expandedIntSize(visibleContentSize));
 }
 
 IntSize ScrollView::layoutSize(VisibleContentRectIncludesScrollbars scrollbarInclusion) const
 {
-    return m_fixedLayoutSize.isEmpty() || !m_useFixedLayout ? unscaledVisibleContentSize(scrollbarInclusion) : m_fixedLayoutSize;
+    return m_fixedLayoutSize.isZero() || !m_useFixedLayout ? unscaledVisibleContentSize(scrollbarInclusion) : m_fixedLayoutSize;
 }
 
 IntSize ScrollView::fixedLayoutSize() const
@@ -221,6 +223,8 @@ IntSize ScrollView::fixedLayoutSize() const
 
 void ScrollView::setFixedLayoutSize(const IntSize& newSize)
 {
+    if (m_fixedLayoutSizeLock)
+        return;
     if (fixedLayoutSize() == newSize)
         return;
     m_fixedLayoutSize = newSize;
@@ -243,6 +247,16 @@ void ScrollView::setUseFixedLayout(bool enable)
     contentsResized();
 }
 
+void ScrollView::setFixedLayoutSizeLock(bool enable)
+{
+    m_fixedLayoutSizeLock = enable;
+}
+
+bool ScrollView::fixedLayoutSizeLock() const
+{
+    return m_fixedLayoutSizeLock;
+}
+
 IntSize ScrollView::contentsSize() const
 {
     return m_contentsSize;