Use float for scroll offset.

third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp

Index: third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
diff --git a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
index d7586cef31542075e0003db3c919905660465742..6349bcd7c8cc73763d625d8ce2692521f2b29b54 100644
--- a/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
+++ b/third_party/WebKit/Source/core/layout/compositing/CompositedLayerMapping.cpp
@@ -1086,9 +1086,10 @@ void CompositedLayerMapping::updateOverflowControlsHostLayerGeometry(
       transformState.flatten();
       hostLayerPosition = LayoutPoint(transformState.lastPlanarPoint());
       if (PaintLayerScrollableArea* scrollableArea =
-              compositingStackingContext->getScrollableArea())
+              compositingStackingContext->getScrollableArea()) {
         hostLayerPosition.move(
-            LayoutSize(scrollableArea->adjustedScrollOffset()));
+            LayoutSize(toFloatSize(scrollableArea->scrollPosition())));
+      }
       hostLayerPosition.move(-stackingOffsetFromLayoutObject);
     }
   } else {
@@ -1195,8 +1196,8 @@ void CompositedLayerMapping::updateScrollingLayerGeometry(
   LayoutBox* layoutBox = toLayoutBox(layoutObject());
   IntRect overflowClipRect =
       enclosingIntRect(layoutBox->overflowClipRect(LayoutPoint()));
-  DoubleSize adjustedScrollOffset =
-      m_owningLayer.getScrollableArea()->adjustedScrollOffset();
+  FloatPoint scrollPosition =
+      m_owningLayer.getScrollableArea()->scrollPosition();
   m_scrollingLayer->setPosition(FloatPoint(
       overflowClipRect.location() - localCompositingBounds.location() +
       roundedIntSize(m_owningLayer.subpixelAccumulation())));
@@ -1223,8 +1224,8 @@ void CompositedLayerMapping::updateScrollingLayerGeometry(
     m_scrollingContentsLayer->setNeedsDisplay();
 
   DoubleSize scrollingContentsOffset(
-      overflowClipRect.location().x() - adjustedScrollOffset.width(),
-      overflowClipRect.location().y() - adjustedScrollOffset.height());
+      overflowClipRect.location().x() - scrollPosition.x(),
+      overflowClipRect.location().y() - scrollPosition.y());
   // The scroll offset change is compared using floating point so that fractional scroll offset
   // change can be propagated to compositor.
   if (scrollingContentsOffset != m_scrollingContentsOffset ||
@@ -1232,9 +1233,8 @@ void CompositedLayerMapping::updateScrollingLayerGeometry(
     bool coordinatorHandlesOffset =
         compositor()->scrollingLayerDidChange(&m_owningLayer);
     m_scrollingContentsLayer->setPosition(
-        coordinatorHandlesOffset
-            ? FloatPoint()
-            : FloatPoint(-toFloatSize(adjustedScrollOffset)));
+        coordinatorHandlesOffset ? FloatPoint()
+                                 : FloatPoint(-toFloatSize(scrollPosition)));
   }
   m_scrollingContentsOffset = scrollingContentsOffset;
 
@@ -2822,9 +2822,10 @@ void CompositedLayerMapping::adjustForCompositedScrolling(
     if (PaintLayerScrollableArea* scrollableArea =
             m_owningLayer.getScrollableArea()) {
       if (scrollableArea->usesCompositedScrolling()) {
-        // Note: this is just the scroll offset, *not* the "adjusted scroll offset". Scroll offset
-        // does not include the origin adjustment. That is instead baked already into offsetFromLayoutObject.
-        DoubleSize scrollOffset = scrollableArea->scrollOffset();
+        // Note: this is the offset from the beginning of flow of the block, not the
+        // offset from the top/left of the overflow rect.  offsetFromLayoutObject adds
+        // the origin offset from top/left to the beginning of flow.
+        ScrollOffset scrollOffset = scrollableArea->scrollOffset();
         offset.expand(-scrollOffset.width(), -scrollOffset.height());
       }
     }