Don't scale fixed container adjustment in pinch virtual viewport.

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/debug/trace_event.h"
 #include "base/debug/trace_event_argument.h"
 #include "base/json/json_reader.h"
 #include "base/strings/stringprintf.h"
@@ skipping 601 matching lines @@
 }
 
 gfx::Vector2dF LayerImpl::FixedContainerSizeDelta() const {
   if (!scroll_clip_layer_)
     return gfx::Vector2dF();
 
   float scale_delta = layer_tree_impl()->page_scale_delta();
   float scale = layer_tree_impl()->page_scale_factor();
 
   gfx::Vector2dF delta_from_scroll = scroll_clip_layer_->bounds_delta();
+
+  // In virtual-viewport mode, we don't need to compensate for pinch zoom or
+  // scale since the fixed container is the outer viewport, which sits below
+  // the page scale.
+  if (layer_tree_impl()->settings().use_pinch_virtual_viewport)
+    return delta_from_scroll;
+
   delta_from_scroll.Scale(1.f / scale);
 
   // The delta-from-pinch component requires some explanation: A viewport of
   // size (w,h) will appear to be size (w/s,h/s) under scale s in the content
   // space. If s -> s' on the impl thread, where s' = s * ds, then the apparent
   // viewport size change in the content space due to ds is:
   //
   // (w/s',h/s') - (w/s,h/s) = (w,h)(1/s' - 1/s) = (w,h)(1 - ds)/(s ds)
   //
   gfx::Vector2dF delta_from_pinch =
@@ skipping 941 matching lines @@
 }
 
 void LayerImpl::NotifyAnimationFinished(
     base::TimeTicks monotonic_time,
     Animation::TargetProperty target_property) {
   if (target_property == Animation::ScrollOffset)
     layer_tree_impl_->InputScrollAnimationFinished();
 }
 
 }  // namespace cc