Make aborted commits inform the scroll delegate.

cc/layers/layer_impl.cc

Index: cc/layers/layer_impl.cc
diff --git a/cc/layers/layer_impl.cc b/cc/layers/layer_impl.cc
index 2b1193370eee237e307ce28f4074ce6a3134ce8c..bfd8f711da06716ac544d3535c301feddd670dcb 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -397,23 +397,22 @@ bool LayerImpl::user_scrollable(ScrollbarOrientation orientation) const {
 }
 
 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() {