SelectionAutoscroll should not happen in user-select:none.

third_party/WebKit/Source/core/input/MouseEventManager.cpp

Index: third_party/WebKit/Source/core/input/MouseEventManager.cpp
diff --git a/third_party/WebKit/Source/core/input/MouseEventManager.cpp b/third_party/WebKit/Source/core/input/MouseEventManager.cpp
index c38ab2fcb8db66b6adc03875a6e1446fdffb617a..4d9a743195e9de7df2541a700887aa4f02a771f7 100644
--- a/third_party/WebKit/Source/core/input/MouseEventManager.cpp
+++ b/third_party/WebKit/Source/core/input/MouseEventManager.cpp
@@ -732,8 +732,13 @@ WebInputEventResult MouseEventManager::handleMouseDraggedEvent(
 
   m_mouseDownMayStartDrag = false;
 
+  m_frame->eventHandler().selectionController().handleMouseDraggedEvent(
+      event, m_mouseDownPos, m_dragStartPos, m_mousePressNode.get(),
+      m_lastKnownMousePosition);
+
   if (m_mouseDownMayStartAutoscroll &&
-      !m_scrollManager->middleClickAutoscrollInProgress()) {
+      !m_scrollManager->middleClickAutoscrollInProgress() &&
+      !m_frame->selection().selectedHTMLForClipboard().isEmpty()) {
     if (AutoscrollController* controller =
             m_scrollManager->autoscrollController()) {
       controller->startAutoscrollForSelection(layoutObject);
@@ -741,9 +746,6 @@ WebInputEventResult MouseEventManager::handleMouseDraggedEvent(
     }
   }
 
-  m_frame->eventHandler().selectionController().handleMouseDraggedEvent(
-      event, m_mouseDownPos, m_dragStartPos, m_mousePressNode.get(),
-      m_lastKnownMousePosition);
   return WebInputEventResult::HandledSystem;
 }