Check frame for nullptr in WebCore::AutoscrollController::animate

The previous solution at https://codereview.chromium.org/2316113003/ does not check
all the frames for nullptr. This patch solves the problem in a more clean and
thorough way.

BUG=361036

Review-Url: https://codereview.chromium.org/2322013002
Cr-Commit-Position: refs/heads/master@{#417399}

third_party/WebKit/Source/core/page/AutoscrollController.cpp

@@ -235,26 +235,24 @@ bool AutoscrollController::panScrollInProgress() const
 
 void AutoscrollController::animate(double)
 {
-    if (!m_autoscrollLayoutObject) {
+    if (!m_autoscrollLayoutObject || !m_autoscrollLayoutObject->frame()) {
         stopAutoscroll();
         return;
     }
 
+    EventHandler& eventHandler = m_autoscrollLayoutObject->frame()->eventHandler();
     switch (m_autoscrollType) {
     case AutoscrollForDragAndDrop:
         if (WTF::monotonicallyIncreasingTime() - m_dragAndDropAutoscrollStartTime > autoscrollDelay)
             m_autoscrollLayoutObject->autoscroll(m_dragAndDropAutoscrollReferencePosition);
         break;
     case AutoscrollForSelection:
-        if (LocalFrame* frame = m_autoscrollLayoutObject->frame()) {
-            EventHandler& eventHandler = frame->eventHandler();
         if (!eventHandler.mousePressed()) {
             stopAutoscroll();
             return;
         }
         eventHandler.updateSelectionForMouseDrag();
         m_autoscrollLayoutObject->autoscroll(eventHandler.lastKnownMousePosition());
-        }
         break;
     case NoAutoscroll:
         break;
@@ -265,12 +263,8 @@ void AutoscrollController::animate(double)
             stopAutoscroll();
             return;
         }
-        if (LocalFrame* frame = m_autoscrollLayoutObject->frame()) {
-            if (FrameView* view = frame->view()) {
-                EventHandler& eventHandler = frame->eventHandler();
+        if (FrameView* view = m_autoscrollLayoutObject->frame()->view())
             updatePanScrollState(view, eventHandler.lastKnownMousePosition());
-            }
-        }
         m_autoscrollLayoutObject->panScroll(m_panScrollStartPos);
         break;
 #endif