Allow objects without scrollbars to be scrollable

Source/core/platform/ScrollAnimator.cpp

Index: Source/core/platform/ScrollAnimator.cpp
diff --git a/Source/core/platform/ScrollAnimator.cpp b/Source/core/platform/ScrollAnimator.cpp
index 2924a2b6252131a508dd6457804c3c14a152f8f4..2b36c18f50074776a2b1cee265bdb65a1fdc2ba8 100644
--- a/Source/core/platform/ScrollAnimator.cpp
+++ b/Source/core/platform/ScrollAnimator.cpp
@@ -76,13 +76,13 @@ void ScrollAnimator::scrollToOffsetWithoutAnimation(const FloatPoint& offset)
 
 bool ScrollAnimator::handleWheelEvent(const PlatformWheelEvent& e)
 {
-    Scrollbar* horizontalScrollbar = m_scrollableArea->horizontalScrollbar();
-    Scrollbar* verticalScrollbar = m_scrollableArea->verticalScrollbar();
+    bool canScrollX = m_scrollableArea->isHorizontallyScrollable();
+    bool canScrollY = m_scrollableArea->isVerticallyScrollable();
 
-    // Accept the event if we have a scrollbar in that direction and can still
+    // Accept the event if we are scrollable in that direction and can still
     // scroll any further.
-    float deltaX = horizontalScrollbar ? e.deltaX() : 0;
-    float deltaY = verticalScrollbar ? e.deltaY() : 0;
+    float deltaX = canScrollX ? e.deltaX() : 0;
+    float deltaY = canScrollY ? e.deltaY() : 0;
 
     bool handled = false;
 
@@ -107,7 +107,13 @@ bool ScrollAnimator::handleWheelEvent(const PlatformWheelEvent& e)
                 if (negative)
                     deltaY = -deltaY;
             }
-            scroll(VerticalScrollbar, granularity, verticalScrollbar->pixelStep(), -deltaY);
+
+            float step = 1;
+            Scrollbar* verticalScrollbar = m_scrollableArea->verticalScrollbar();
+            if (verticalScrollbar)
+                step = verticalScrollbar->pixelStep();
+
+            scroll(VerticalScrollbar, granularity, step, -deltaY);
         }
 
         if (deltaX) {
@@ -117,7 +123,13 @@ bool ScrollAnimator::handleWheelEvent(const PlatformWheelEvent& e)
                 if (negative)
                     deltaX = -deltaX;
             }
-            scroll(HorizontalScrollbar, granularity, horizontalScrollbar->pixelStep(), -deltaX);
+
+            float step = 1;
+            Scrollbar* horizontalScrollbar = m_scrollableArea->horizontalScrollbar();
+            if (horizontalScrollbar)
+                step = horizontalScrollbar->pixelStep();
+
+            scroll(HorizontalScrollbar, granularity, step, -deltaX);
         }
     }
     return handled;