Use the physical-pixel space for native IME on linux platform.

ui/views/controls/textfield/textfield.cc

Index: ui/views/controls/textfield/textfield.cc
diff --git a/ui/views/controls/textfield/textfield.cc b/ui/views/controls/textfield/textfield.cc
index 1de38cc04e5358d0757c2ed5a3036a766b8d10c5..0297b2c1840fac9b8dc1e016a60f63599cdd5a98 100644
--- a/ui/views/controls/textfield/textfield.cc
+++ b/ui/views/controls/textfield/textfield.cc
@@ -1322,6 +1322,11 @@ bool Textfield::CanComposeInline() const {
   return true;
 }
 
+float Textfield::GetScaleFactor() const {
+  return display::Screen::GetScreen()->GetDisplayNearestWindow(
+      GetWidget()->GetNativeWindow()).device_scale_factor();
+}
+
 gfx::Rect Textfield::GetCaretBounds() const {
   gfx::Rect rect = GetRenderText()->GetUpdatedCursorBounds();
   ConvertRectToScreen(this, &rect);