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

ui/views/controls/textfield/textfield.cc

 // Copyright (c) 2012 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/views/controls/textfield/textfield.h"
 
 #include <string>
 #include <utility>
 
 #include "base/strings/utf_string_conversions.h"
@@ skipping 1304 matching lines @@
 }
 
 int Textfield::GetTextInputFlags() const {
   return text_input_flags_;
 }
 
 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);
   return rect;
 }
 
 bool Textfield::GetCompositionCharacterBounds(uint32_t index,
                                               gfx::Rect* rect) const {
   DCHECK(rect);
   if (!HasCompositionText())
@@ skipping 722 matching lines @@
 }
 
 void Textfield::OnCursorBlinkTimerFired() {
   DCHECK(ShouldBlinkCursor());
   gfx::RenderText* render_text = GetRenderText();
   render_text->set_cursor_visible(!render_text->cursor_visible());
   RepaintCursor();
 }
 
 }  // namespace views