Fix premature termination of scroll animations while selecting text.

third_party/WebKit/Source/core/frame/RootFrameViewport.cpp

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/frame/RootFrameViewport.h"
 
 #include "core/frame/FrameView.h"
 #include "core/layout/ScrollAlignment.h"
 #include "platform/geometry/DoubleRect.h"
 #include "platform/geometry/FloatRect.h"
@@ skipping 91 matching lines @@
         layoutViewport().scrollAnimator().currentPosition(),
         layoutViewport().visibleContentRect().size());
     LayoutRect visualRectInContent = LayoutRect(
         scrollOffsetFromScrollAnimators(),
         visualViewport().visibleContentRect().size());
 
     // Intersect layout and visual rects to exclude the scrollbar from the view rect.
     LayoutRect viewRectInContent = intersection(visualRectInContent, frameRectInContent);
     LayoutRect targetViewport =
         ScrollAlignment::getRectToExpose(viewRectInContent, rectInContent, alignX, alignY);
-    DoublePoint targetOffset(targetViewport.x(), targetViewport.y());
-
-    setScrollPosition(targetOffset, scrollType, ScrollBehaviorInstant);
+    if (targetViewport != viewRectInContent)
+        setScrollPosition(DoublePoint(targetViewport.x(), targetViewport.y()), scrollType);
 
     // RootFrameViewport only changes the viewport relative to the document so we can't change the input
     // rect's location relative to the document origin.
     return rectInContent;
 }
 
 void RootFrameViewport::setScrollOffset(const DoublePoint& offset, ScrollType scrollType)
 {
     distributeScrollBetweenViewports(DoublePoint(offset), scrollType, ScrollBehaviorInstant);
 }
@@ skipping 211 matching lines @@
 }
 
 DEFINE_TRACE(RootFrameViewport)
 {
     visitor->trace(m_visualViewport);
     visitor->trace(m_layoutViewport);
     ScrollableArea::trace(visitor);
 }
 
 } // namespace blink