Add back the truncation of scroll_delta

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/json/json_reader.h"
 #include "base/strings/stringprintf.h"
 #include "base/trace_event/trace_event.h"
 #include "base/trace_event/trace_event_argument.h"
@@ skipping 1119 matching lines @@
 }
 
 void LayerImpl::PushScrollOffsetFromMainThreadAndClobberActiveValue(
     const gfx::ScrollOffset& scroll_offset) {
   scroll_offset_->set_clobber_active_value();
   PushScrollOffset(&scroll_offset);
 }
 
 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() {
   if (scroll_offset_delegate_) {
     SetCurrentScrollOffset(
         gfx::ScrollOffset(scroll_offset_delegate_->GetCurrentScrollOffset()));
   }
 }
 
 gfx::ScrollOffset LayerImpl::CurrentScrollOffset() const {
@@ skipping 453 matching lines @@
   gfx::Transform scaled_draw_transform =
       draw_properties_.target_space_transform;
   scaled_draw_transform.Scale(SK_MScalar1 / scale, SK_MScalar1 / scale);
   gfx::Size scaled_content_bounds =
       gfx::ToCeiledSize(gfx::ScaleSize(content_bounds(), scale));
   return MathUtil::MapEnclosingClippedRect(scaled_draw_transform,
                                            gfx::Rect(scaled_content_bounds));
 }
 
 }  // namespace cc