Notify ProgrammaticScrollAnimator about scroll layer destruction

Source/platform/scroll/ProgrammaticScrollAnimator.cpp

 // Copyright 2014 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 "config.h"
 #include "platform/scroll/ProgrammaticScrollAnimator.h"
 
 #include "platform/geometry/IntPoint.h"
 #include "platform/graphics/GraphicsLayer.h"
 #include "platform/scroll/ScrollableArea.h"
@@ skipping 145 matching lines @@
         if (!sentToCompositor) {
             m_runState = RunState::RunningOnMainThread;
             if (!m_scrollableArea->scheduleAnimation()) {
                 m_scrollableArea->notifyScrollPositionChanged(IntPoint(m_targetOffset.x(), m_targetOffset.y()));
                 resetAnimationState();
             }
         }
     }
 }
 
+void ProgrammaticScrollAnimator::layerForCompositedScrollingDidChange()
+{
+    // If the composited scrolling layer is lost during a composited animation,
+    // continue the animation on the main thread.
+    if (m_runState == RunState::RunningOnCompositor && !m_scrollableArea->layerForScrolling()) {
+        m_runState = RunState::RunningOnMainThread;
+        m_compositorAnimationId = 0;
+        m_compositorAnimationGroupId = 0;
+        m_animationCurve->setInitialValue(FloatPoint(m_scrollableArea->scrollPosition()));
+        m_scrollableArea->registerForAnimation();
+        if (!m_scrollableArea->scheduleAnimation()) {
+            resetAnimationState();
+            m_scrollableArea->notifyScrollPositionChanged(IntPoint(m_targetOffset.x(), m_targetOffset.y()));
+        }
+    }
+}
+
 void ProgrammaticScrollAnimator::notifyCompositorAnimationFinished(int groupId)
 {
     if (m_compositorAnimationGroupId != groupId)
         return;
 
     m_compositorAnimationId = 0;
     m_compositorAnimationGroupId = 0;
 
     switch (m_runState) {
     case RunState::Idle:
     case RunState::RunningOnMainThread:
         ASSERT_NOT_REACHED();
         break;
     case RunState::WaitingToSendToCompositor:
         break;
     case RunState::RunningOnCompositor:
     case RunState::WaitingToCancelOnCompositor:
         resetAnimationState();
     }
 }
 
 } // namespace blink