Should be tracking scrolls for Outer, and not Inner, scroll layer.

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/numerics/safe_conversions.h"
 #include "base/strings/stringprintf.h"
 #include "base/trace_event/trace_event.h"
@@ skipping 1503 matching lines @@
   } else {
     float visible_ratio = clip_rect.height() / scroll_rect.height();
     bool y_offset_did_change =
         scrollbar_layer->SetCurrentPos(current_offset.y());
     scrollbar_needs_animation |= y_offset_did_change;
     scrollbar_needs_animation |=
         scrollbar_layer->SetMaximum(scroll_rect.height() - clip_rect.height());
     scrollbar_needs_animation |=
         scrollbar_layer->SetVisibleToTotalLengthRatio(visible_ratio);
     if (y_offset_did_change && layer_tree_impl()->IsActiveTree() &&
-        this == layer_tree_impl()->InnerViewportScrollLayer()) {
+        this == layer_tree_impl()->OuterViewportScrollLayer()) {
       TRACE_COUNTER_ID1("cc", "scroll_offset_y", this->id(),
                         current_offset.y());
     }
   }
   if (scrollbar_needs_animation) {
     layer_tree_impl()->set_needs_update_draw_properties();
     // TODO(wjmaclean) The scrollbar animator for the pinch-zoom scrollbars
     // should activate for every scroll on the main frame, not just the
     // scrolls that move the pinch virtual viewport (i.e. trigger from
     // either inner or outer viewport).
@@ skipping 299 matching lines @@
   }
 
   // TODO(enne): the transform needs to come from property trees instead of
   // draw properties.
   gfx::Vector2dF transform_scales = MathUtil::ComputeTransform2dScaleComponents(
       draw_properties().target_space_transform, default_scale);
   return std::max(transform_scales.x(), transform_scales.y());
 }
 
 }  // namespace cc