Permit MaterialDesignController to make IO call

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 "base/trace_event/trace_event.h"
 #include "ui/base/material_design/material_design_controller.h"
 #include "ui/base/ui_base_switches.h"
 
 #if defined(OS_CHROMEOS)
 #include "ui/base/touch/touch_device.h"
 #include "ui/events/devices/device_data_manager.h"
 
 #if defined(USE_OZONE)
 #include <fcntl.h>
 
 #include "base/files/file_enumerator.h"
+#include "base/threading/thread_restrictions.h"
 #include "ui/events/ozone/evdev/event_device_info.h"
 #endif  // defined(USE_OZONE)
 
 #endif  // defined(OS_CHROMEOS)
 
 namespace ui {
 
 bool MaterialDesignController::is_mode_initialized_ = false;
 
 MaterialDesignController::Mode MaterialDesignController::mode_ =
@@ skipping 44 matching lines @@
 }
 
 // static
 bool MaterialDesignController::IsSecondaryUiMaterial() {
   return IsModeMaterial() && include_secondary_ui_;
 }
 
 // static
 MaterialDesignController::Mode MaterialDesignController::DefaultMode() {
 #if defined(OS_CHROMEOS)
+  // If a scan of available devices has already completed, use material-hybrid
+  // if a touchscreen is present.
   if (DeviceDataManager::HasInstance() &&
       DeviceDataManager::GetInstance()->device_lists_complete()) {
     return GetTouchScreensAvailability() == TouchScreensAvailability::ENABLED
                ? MATERIAL_HYBRID
                : MATERIAL_NORMAL;
   }
 
 #if defined(USE_OZONE)
+  // Otherwise perform our own scan to determine the presence of a touchscreen.
+  // Note this is a one-time call that occurs during device startup or restart.
+  base::ThreadRestrictions::ScopedAllowIO allow_io;
   base::FileEnumerator file_enum(
       base::FilePath(FILE_PATH_LITERAL("/dev/input")), false,
       base::FileEnumerator::FILES, FILE_PATH_LITERAL("event*[0-9]"));
   for (base::FilePath path = file_enum.Next(); !path.empty();
        path = file_enum.Next()) {
     EventDeviceInfo devinfo;
     int fd = open(path.value().c_str(), O_RDWR | O_NONBLOCK | O_CLOEXEC);
     if (fd >= 0) {
       if (devinfo.Initialize(fd, path) && devinfo.HasTouchscreen()) {
         close(fd);
@@ skipping 16 matching lines @@
   is_mode_initialized_ = false;
 }
 
 // static
 void MaterialDesignController::SetMode(MaterialDesignController::Mode mode) {
   mode_ = mode;
   is_mode_initialized_ = true;
 }
 
 }  // namespace ui