Use default shadow elevation.

components/exo/shell_surface.cc

 // Copyright 2015 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 "components/exo/shell_surface.h"
 
 #include <algorithm>
 
 #include "ash/common/frame/custom_frame_view_ash.h"
 #include "ash/common/shelf/wm_shelf.h"
@@ skipping 1469 matching lines @@
       ((widget_->IsFullscreen() || widget_->IsMaximized()) ||
        underlay_capture_events) &&
       ash::wm::GetWindowState(window)->allow_set_bounds_direct() &&
       window->layer()->GetTargetTransform().IsIdentity();
 
   if (!shadow_enabled_ && !black_background_enabled) {
     wm::SetShadowElevation(window, wm::ShadowElevation::NONE);
     if (shadow_underlay_)
       shadow_underlay_->Hide();
   } else {
-    wm::SetShadowElevation(window, wm::ShadowElevation::MEDIUM);
+    wm::SetShadowElevation(window, wm::ShadowElevation::DEFAULT);
     gfx::Rect shadow_content_bounds =
         gfx::ScaleToEnclosedRect(shadow_content_bounds_, 1.f / scale_);
 
     // Convert from screen to display coordinates.
     if (!shadow_content_bounds.IsEmpty()) {
       gfx::Point origin = shadow_content_bounds.origin() - origin_offset_;
       wm::ConvertPointFromScreen(window->parent(), &origin);
       shadow_content_bounds.set_origin(origin);
     }
 
@@ skipping 120 matching lines @@
     // small style shadow for them.
     if (!activatable_)
       shadow->SetElevation(wm::ShadowElevation::SMALL);
     // We don't have rounded corners unless frame is enabled.
     if (!frame_enabled_)
       shadow->SetRoundedCornerRadius(0);
   }
 }
 
 }  // namespace exo