Refactor ScrollableArea::setScrollPosition.

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 b59cf4626abb3a6e4380f5724f7e55c2d0214412..bf2bbdc558be98055fb006d193dae454530e77fe 100644
--- a/third_party/WebKit/Source/core/layout/LayoutBox.cpp
+++ b/third_party/WebKit/Source/core/layout/LayoutBox.cpp
@@ -256,18 +256,20 @@ void LayoutBox::styleDidChange(StyleDifference diff,
   }
 
   // If our zoom factor changes and we have a defined scrollLeft/Top, we need to adjust that value into the
-  // new zoomed coordinate space.
+  // new zoomed coordinate space.  Note that the new scroll position may be outside the normal min/max
+  // range of the scrollable area, which is weird but OK, because the scrollable area will update its
+  // min/max in updateAfterLayout().
   if (hasOverflowClip() && oldStyle &&
       oldStyle->effectiveZoom() != newStyle.effectiveZoom()) {
     PaintLayerScrollableArea* scrollableArea = this->getScrollableArea();
     ASSERT(scrollableArea);
-    if (int left = scrollableArea->scrollXOffset()) {
-      left = (left / oldStyle->effectiveZoom()) * newStyle.effectiveZoom();
-      scrollableArea->scrollToXOffset(left);
-    }
-    if (int top = scrollableArea->scrollYOffset()) {
-      top = (top / oldStyle->effectiveZoom()) * newStyle.effectiveZoom();
-      scrollableArea->scrollToYOffset(top);
+    // We use scrollPosition() rather than offsetFromOrigin(), because scrollPosition is the distance
+    // from the beginning of flow for the box, which is the dimension we want to preserve.
+    DoublePoint oldPosition = scrollableArea->scrollPositionDouble();
+    if (oldPosition.x() || oldPosition.y()) {
+      DoublePoint newPosition = oldPosition.scaledBy(newStyle.effectiveZoom() /
+                                                     oldStyle->effectiveZoom());
+      scrollableArea->setScrollPositionUnconditionally(newPosition);
     }
   }
 
@@ -512,13 +514,15 @@ LayoutUnit LayoutBox::scrollHeight() const {
 }
 
 LayoutUnit LayoutBox::scrollLeft() const {
-  return hasOverflowClip() ? LayoutUnit(getScrollableArea()->scrollXOffset())
-                           : LayoutUnit();
+  return hasOverflowClip()
+             ? LayoutUnit(getScrollableArea()->offsetFromOrigin().width())
+             : LayoutUnit();
 }
 
 LayoutUnit LayoutBox::scrollTop() const {
-  return hasOverflowClip() ? LayoutUnit(getScrollableArea()->scrollYOffset())
-                           : LayoutUnit();
+  return hasOverflowClip()
+             ? LayoutUnit(getScrollableArea()->offsetFromOrigin().height())
+             : LayoutUnit();
 }
 
 int LayoutBox::pixelSnappedScrollWidth() const {
@@ -539,18 +543,24 @@ void LayoutBox::setScrollLeft(LayoutUnit newLeft) {
   // does, presumably this code does as well.
   DisableCompositingQueryAsserts disabler;
 
-  if (hasOverflowClip())
-    getScrollableArea()->scrollToXOffset(newLeft, ScrollOffsetClamped,
-                                         ScrollBehaviorAuto);
+  if (!hasOverflowClip())
+    return;
+
+  PaintLayerScrollableArea* scrollableArea = getScrollableArea();
+  DoubleSize newOffset(newLeft, scrollableArea->offsetFromOrigin().height());
+  scrollableArea->scrollToOffsetFromOrigin(newOffset, ScrollBehaviorAuto);
 }
 
 void LayoutBox::setScrollTop(LayoutUnit newTop) {
   // Hits in compositing/overflow/do-not-assert-on-invisible-composited-layers.html
   DisableCompositingQueryAsserts disabler;
 
-  if (hasOverflowClip())
-    getScrollableArea()->scrollToYOffset(newTop, ScrollOffsetClamped,
-                                         ScrollBehaviorAuto);
+  if (!hasOverflowClip())
+    return;
+
+  PaintLayerScrollableArea* scrollableArea = getScrollableArea();
+  DoubleSize newOffset(scrollableArea->offsetFromOrigin().width(), newTop);
+  scrollableArea->scrollToOffsetFromOrigin(newOffset, ScrollBehaviorAuto);
 }
 
 void LayoutBox::scrollToOffset(const DoubleSize& offset,
@@ -559,9 +569,10 @@ void LayoutBox::scrollToOffset(const DoubleSize& offset,
   // does, presumably this code does as well.
   DisableCompositingQueryAsserts disabler;
 
-  if (hasOverflowClip())
-    getScrollableArea()->scrollToOffset(offset, ScrollOffsetClamped,
-                                        scrollBehavior);
+  if (!hasOverflowClip())
+    return;
+
+  getScrollableArea()->scrollToOffsetFromOrigin(offset, scrollBehavior);
 }
 
 // Returns true iff we are attempting an autoscroll inside an iframe with scrolling="no".
@@ -1076,8 +1087,7 @@ void LayoutBox::middleClickAutoscroll(const IntPoint& sourcePoint) {
   scroll(ScrollByPixel, FloatSize(adjustedScrollDelta(delta)));
 }
 
-void LayoutBox::scrollByRecursively(const DoubleSize& delta,
-                                    ScrollOffsetClamping clamp) {
+void LayoutBox::scrollByRecursively(const DoubleSize& delta) {
   if (delta.isZero())
     return;
 
@@ -1089,15 +1099,15 @@ void LayoutBox::scrollByRecursively(const DoubleSize& delta,
     PaintLayerScrollableArea* scrollableArea = this->getScrollableArea();
     ASSERT(scrollableArea);
 
-    DoubleSize newScrollOffset = scrollableArea->adjustedScrollOffset() + delta;
-    scrollableArea->scrollToOffset(newScrollOffset, clamp);
+    DoubleSize newScrollOffset = scrollableArea->offsetFromOrigin() + delta;
+    scrollableArea->scrollToOffsetFromOrigin(newScrollOffset);
 
     // If this layer can't do the scroll we ask the next layer up that can scroll to try
     DoubleSize remainingScrollOffset =
-        newScrollOffset - scrollableArea->adjustedScrollOffset();
+        newScrollOffset - scrollableArea->offsetFromOrigin();
     if (!remainingScrollOffset.isZero() && parent()) {
       if (LayoutBox* scrollableBox = enclosingScrollableBox())
-        scrollableBox->scrollByRecursively(remainingScrollOffset, clamp);
+        scrollableBox->scrollByRecursively(remainingScrollOffset);
 
       LocalFrame* frame = this->frame();
       if (frame && frame->page())
@@ -1135,7 +1145,7 @@ IntSize LayoutBox::scrolledContentOffset() const {
   ASSERT(hasLayer());
   // FIXME: Return DoubleSize here. crbug.com/414283.
   PaintLayerScrollableArea* scrollableArea = getScrollableArea();
-  IntSize result = flooredIntSize(scrollableArea->scrollOffset()) +
+  IntSize result = flooredIntSize(scrollableArea->scrollPosition()) +
                    originAdjustmentForScrollbars();
   if (isHorizontalWritingMode() &&
       shouldPlaceBlockDirectionScrollbarOnLogicalLeft())