Make the header/content separator into a hairline for apps in hidpi

ash/frame/header_painter_util.cc

 // Copyright 2014 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 "ash/frame/header_painter_util.h"
 
 #include <algorithm>
 
 #include "ui/aura/window.h"
 #include "ui/compositor/layer.h"
@@ skipping 56 matching lines @@
 }
 
 // static
 gfx::Rect HeaderPainterUtil::GetTitleBounds(
     const views::View* icon,
     const views::View* caption_button_container,
     const gfx::FontList& title_font_list) {
   int x = icon ?
       icon->bounds().right() + kTitleIconOffsetX : kTitleNoIconOffsetX;
   int height = title_font_list.GetHeight();
-  int y = std::max(
-      0,
-      static_cast<int>(std::ceil(
-          (caption_button_container->height() - height) / 2.0f)));
+  // Floor when computing the center of |caption_button_container| and when
+  // computing the center of the text.
+  int y = std::max(0, (caption_button_container->height() / 2) - (height / 2));
   int width = std::max(
       0, caption_button_container->x() - kTitleCaptionButtonSpacing - x);
   return gfx::Rect(x, y, width, height);
 }
 
 // static
 bool HeaderPainterUtil::CanAnimateActivation(views::Widget* widget) {
   // Do not animate the header if the parent (e.g.
   // kShellWindowId_DefaultContainer) is already animating. All of the
   // implementers of HeaderPainter animate activation by continuously painting
   // during the animation. This gives the parent's animation a slower frame
   // rate.
   // TODO(sky): Expose a better way to determine this rather than assuming the
   // parent is a toplevel container.
   aura::Window* window = widget->GetNativeWindow();
   if (!window->parent())
     return true;
 
   ui::LayerAnimator* parent_layer_animator =
       window->parent()->layer()->GetAnimator();
   return !parent_layer_animator->IsAnimatingProperty(
              ui::LayerAnimationElement::OPACITY) &&
          !parent_layer_animator->IsAnimatingProperty(
              ui::LayerAnimationElement::VISIBILITY);
 }
 
 }  // namespace ash