Add tests for InputDevice/TouchscreenDevice StructTraits.

ui/events/devices/mojo/input_device_struct_traits.cc

Index: ui/events/devices/mojo/input_device_struct_traits.cc
diff --git a/ui/events/devices/mojo/input_device_struct_traits.cc b/ui/events/devices/mojo/input_device_struct_traits.cc
index afab8208d5c42f1df702a70bbac4678a8d1c00b3..8d5a9f60af37c13a8b8971b71c89966dbc19f462 100644
--- a/ui/events/devices/mojo/input_device_struct_traits.cc
+++ b/ui/events/devices/mojo/input_device_struct_traits.cc
@@ -55,7 +55,7 @@ bool StructTraits<ui::mojom::InputDevice, ui::InputDevice>::Read(
   if (!data.ReadName(&out->name))
     return false;
 
-  base::StringPiece sys_path_string;
+  std::string sys_path_string;
   if (!data.ReadSysPath(&sys_path_string))
     return false;
   out->sys_path = base::FilePath::FromUTF8Unsafe(sys_path_string);