Move X11 device processing to worker threads

ui/events/devices/device_util_linux.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 "ui/events/devices/device_util_linux.h"
 
 #include <string>
 
 #include "base/files/file_enumerator.h"
 #include "base/files/file_path.h"
+#include "base/message_loop/message_loop.h"
 #include "base/strings/string_util.h"
 
 namespace ui {
 
+// We consider the touchscreen to be internal if it is an I2c device. We search
+// all the dev input nodes registered by I2C devices to see if we can find
+// eventXXX.
 bool IsTouchscreenInternal(const base::FilePath& path) {
+  DCHECK(!base::MessageLoopForUI::IsCurrent());
   std::string event_node = path.BaseName().value();
   if (event_node.empty() || !StartsWithASCII(event_node, "event", false))
     return false;
 
   // Extract id "XXX" from "eventXXX"
   std::string event_node_id = event_node.substr(5);
 
   // I2C input device registers its dev input node at
   // /sys/bus/i2c/devices/*/input/inputXXX/eventXXX
   base::FileEnumerator i2c_enum(
@@ skipping 11 matching lines @@
          input = input_enum.Next()) {
       if (input.BaseName().value().substr(5) == event_node_id)
         return true;
     }
   }
 
   return false;
 }
 
 }  // namespace