[MD] turn on MD by default for desktop linux

ui/base/material_design/material_design_controller.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 <string>
 
 #include "base/command_line.h"
 #include "base/logging.h"
 #include "ui/base/material_design/material_design_controller.h"
 #include "ui/base/ui_base_switches.h"
@@ skipping 26 matching lines @@
 #if defined(OS_CHROMEOS)
   // TODO(tdanderson): Enable hybrid by default for touchscreen devices.
   //                   See crbug.com/588880.
   const std::string board = base::SysInfo::GetLsbReleaseBoard();
   if (base::StartsWith(board, "link", base::CompareCase::SENSITIVE) ||
       base::StartsWith(board, "veyron_minnie", base::CompareCase::SENSITIVE) ||
       base::StartsWith(board, "samus", base::CompareCase::SENSITIVE)) {
     return Mode::MATERIAL_HYBRID;
   }
   return Mode::MATERIAL_NORMAL;
+#elif defined(OS_LINUX)
+  return Mode::MATERIAL_NORMAL;
 #else
   return Mode::NON_MATERIAL;
 #endif  // defined(OS_CHROMEOS)
 }
 
 void MaterialDesignController::InitializeMode() {
 #if !defined(ENABLE_TOPCHROME_MD)
   SetMode(Mode::NON_MATERIAL);
 #else
   const std::string switch_value =
@@ skipping 22 matching lines @@
       MaterialDesignController::Mode::NON_MATERIAL);
   is_mode_initialized_ = false;
 }
 
 void MaterialDesignController::SetMode(MaterialDesignController::Mode mode) {
   mode_ = mode;
   is_mode_initialized_ = true;
 }
 
 }  // namespace ui