Make aborted commits inform the scroll delegate.

cc/layers/layer_impl.cc

 // Copyright 2012 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 "cc/layers/layer_impl.h"
 
 #include "base/debug/trace_event.h"
 #include "base/debug/trace_event_argument.h"
 #include "base/json/json_reader.h"
 #include "base/strings/stringprintf.h"
@@ skipping 379 matching lines @@
 void LayerImpl::SetScrollClipLayer(int scroll_clip_layer_id) {
   scroll_clip_layer_ = layer_tree_impl()->LayerById(scroll_clip_layer_id);
 }
 
 bool LayerImpl::user_scrollable(ScrollbarOrientation orientation) const {
   return (orientation == HORIZONTAL) ? user_scrollable_horizontal_
                                      : user_scrollable_vertical_;
 }
 
 void LayerImpl::ApplySentScrollDeltasFromAbortedCommit() {
+  if (sent_scroll_delta_.IsZero())
+    return;
+
   // Pending tree never has sent scroll deltas
   DCHECK(layer_tree_impl()->IsActiveTree());
 
+  // The combination of pending tree and aborted commits with impl scrolls
+  // shouldn't happen; we don't know how to update its deltas correctly.
+  DCHECK(!layer_tree_impl()->FindPendingTreeLayerById(id()));
+
   // Apply sent scroll deltas to scroll position / scroll delta as if the
   // main thread had applied them and then committed those values.
-  //
-  // This function should not change the total scroll offset; it just shifts
-  // some of the scroll delta to the scroll offset.  Therefore, adjust these
-  // variables directly rather than calling the scroll offset delegate to
-  // avoid sending it multiple spurious calls.
-  //
-  // Because of the way scroll delta is calculated with a delegate, this will
-  // leave the total scroll offset unchanged on this layer regardless of
-  // whether a delegate is being used.
-  scroll_offset_ += gfx::ScrollOffset(sent_scroll_delta_);
-  scroll_delta_ -= sent_scroll_delta_;
-  sent_scroll_delta_ = gfx::Vector2dF();
+  SetScrollOffsetAndDelta(
+      scroll_offset_ + gfx::ScrollOffset(sent_scroll_delta_),
+      ScrollDelta() - sent_scroll_delta_);
+  SetSentScrollDelta(gfx::Vector2dF());
 }
 
 void LayerImpl::ApplyScrollDeltasSinceBeginMainFrame() {
   // Only the pending tree can have missing scrolls.
   DCHECK(layer_tree_impl()->IsPendingTree());
   if (!scrollable())
     return;
 
   // Pending tree should never have sent scroll deltas.
   DCHECK(sent_scroll_delta().IsZero());
@@ skipping 1162 matching lines @@
 
 void LayerImpl::NotifyAnimationFinished(
     base::TimeTicks monotonic_time,
     Animation::TargetProperty target_property,
     int group) {
   if (target_property == Animation::ScrollOffset)
     layer_tree_impl_->InputScrollAnimationFinished();
 }
 
 }  // namespace cc