Add back the truncation of scroll_delta

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 b34948c5d6c633d5dd918996bd3f8bb767331d0f..0b54efafb37a76a0548c88ce7bf5fc9f0f0aadf4 100644
--- a/cc/layers/layer_impl.cc
+++ b/cc/layers/layer_impl.cc
@@ -1137,7 +1137,20 @@ void LayerImpl::PushScrollOffsetFromMainThreadAndClobberActiveValue(
 
 gfx::ScrollOffset LayerImpl::PullDeltaForMainThread() {
   RefreshFromScrollDelegate();
-  return scroll_offset_->PullDeltaForMainThread();
+
+  // TODO(miletus): Remove all this temporary flooring machinery when
+  // Blink fully supports fractional scrolls.
+  gfx::ScrollOffset current_offset = CurrentScrollOffset();
+  gfx::Vector2dF current_delta = ScrollDelta();
+  gfx::Vector2dF floored_delta(floor(current_delta.x()),
+                               floor(current_delta.y()));
+  gfx::Vector2dF diff_delta = floored_delta - current_delta;
+  gfx::ScrollOffset tmp_offset = ScrollOffsetWithDelta(current_offset,
+                                                       diff_delta);
+  scroll_offset_->SetCurrent(tmp_offset);
+  gfx::ScrollOffset delta = scroll_offset_->PullDeltaForMainThread();
+  scroll_offset_->SetCurrent(current_offset);
+  return delta;
 }
 
 void LayerImpl::RefreshFromScrollDelegate() {