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..9081fa581d8db15a02682a163ac4d43700b71728 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -402,18 +402,10 @@ void LayerImpl::ApplySentScrollDeltasFromAbortedCommit() {
 
   // 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_);

[bokan, 2014/10/29 23:55:42]

SetScrollOffsetAndDelta sets the unsent delta on the twin layer in the pending
tree, will that now remove the sent delta twice?

[aelias_OOO_until_Jul13, 2014/10/30 01:46:55]

Empirically I don't see any bugs if I try scrolling on continuously invalidating
pages.  It seems to be the case that a pending tree never exists when a commit
is aborted, otherwise strangeness would ensue already since nothing in the
commit abort flow updates the pending tree.  Enne, is that a safe assumption?

+  SetSentScrollDelta(gfx::Vector2dF());
 }
 
 void LayerImpl::ApplyScrollDeltasSinceBeginMainFrame() {