Chrome Version       : 52.0.2743.82
OS Version: OS X 10.11.6

ScrollView::ScrollToOffset currently invokes OnLayerScrolled whenever the scroll offset changes. OnLayerScrolled is responsible for updating the position of the header row and scrollbars.

When input events are routed to the cc:InputHandler directly to scroll the layer (also, e.g., for smooth scrolling animations and elasticity rebound), ScrollToOffset isn't invoked and changes go directly to OnLayerScrolled. But this happens asynchronously, and most ScrollView tests don't expect this for things like ScrollRectToVisible.

So for now, OnLayerScrolled will get invoked multiple times each frame if ScrollToOffset is used. ScrollToOffset soon won't be used for the high-throughput trackpad events on Mac since they will get routed to the InputHandler. But for other scrolling codepaths we can save some cycles by not calling OnLayerScrolled in ScrollToOffset, and instead just coalesce everything when the scroll is committed.


context: https://codereview.chromium.org/2188133002/

void ScrollView::ScrollToOffset(const gfx::ScrollOffset& offset) {
  if (ScrollsWithLayers()) {
    contents_->layer()->SetScrollOffset(offset);

    // TODO(tapted): Remove this call to OnLayerScrolled(). It's unnecessary,
    // but will only be invoked (asynchronously) when a Compositor is present
    // and commits a frame, which isn't true in some tests.
    OnLayerScrolled();
  } else {
    contents_->SetPosition(gfx::Point(-offset.x(), -offset.y()));
    ScrollHeader();
  }
}