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

ui/base/ime/text_input_client.h

 // 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.
 
 #ifndef UI_BASE_IME_TEXT_INPUT_CLIENT_H_
 #define UI_BASE_IME_TEXT_INPUT_CLIENT_H_
 
 #include <stddef.h>
 #include <stdint.h>
 
@@ skipping 63 matching lines @@
   virtual base::i18n::TextDirection GetTextDirection() const = 0;
 
   // Returns the current text input flags, which is a bit map of
   // WebTextInputType defined in blink. This is valid only for web input fileds;
   // it will return TEXT_INPUT_FLAG_NONE for native input fields.
   virtual int GetTextInputFlags() const = 0;
 
   // Returns if the client supports inline composition currently.
   virtual bool CanComposeInline() const = 0;
 
+  // Returns the scale factor of the screen in which the view of this
+  // TextInputClient has been located.
+  // This is used in the platform-dependent InputMethod implementations, on
+  // which the native IME requires the non-dip coordinates from
+  // GetCaretBounds, etc.
+  virtual float GetScaleFactor() const = 0;

[sadrul, 2016/12/22 01:30:22]

Unfortunately, there are several types of scale factors (device scale factor, ui
scale factor, page scale factor etc.). So I would suggest calling this
GetDeviceScaleFactor()

[Shu Chen, 2016/12/22 03:02:27]

Done. 
I've removed the GetScaleFactor method.

+
   // Returns current caret (insertion point) bounds in the universal screen
-  // coordinates. If there is selection, then the selection bounds will be
-  // returned.
-  // Note: On Windows, the returned value is supposed to be DIP (Density
-  // Independent Pixel).
-  // TODO(ime): Have a clear spec whether the returned value is DIP or not.
-  // http://crbug.com/360334
+  // coordinates in DIP (Density Independent Pixel).
+  // If there is selection, then the selection bounds will be returned.
   virtual gfx::Rect GetCaretBounds() const = 0;
 
   // Retrieves the composition character boundary rectangle in the universal
-  // screen coordinates. The |index| is zero-based index of character position
-  // in composition text.
+  // screen coordinates in DIP (Density Independent Pixel).
+  // The |index| is zero-based index of character position in composition text.
   // Returns false if there is no composition text or |index| is out of range.
   // The |rect| is not touched in the case of failure.
-  // Note: On Windows, the returned value is supposed to be DIP
-  // (Density Independent Pixel).
-  // TODO(ime): Have a clear spec whether the returned value is DIP or not.
-  // http://crbug.com/360334
   virtual bool GetCompositionCharacterBounds(uint32_t index,
                                              gfx::Rect* rect) const = 0;
 
   // Returns true if there is composition text.
   virtual bool HasCompositionText() const = 0;
 
   // Document content operations ----------------------------------------------
 
   // Retrieves the UTF-16 based character range containing accessible text in
   // the View. It must cover the composition and selection range.
@@ skipping 43 matching lines @@
   virtual bool ChangeTextDirectionAndLayoutAlignment(
       base::i18n::TextDirection direction) = 0;
 
   // Deletes the current selection plus the specified number of characters
   // before and after the selection or caret. This function should be used
   // instead of calling DeleteRange with GetSelectionRange, because
   // GetSelectionRange may not be the latest value due to asynchronous of IPC
   // between browser and renderer.
   virtual void ExtendSelectionAndDelete(size_t before, size_t after) = 0;
 
-  // Ensure the caret is not in |rect|.  |rect| is in screen coordinates and
-  // may extend beyond the bounds of this TextInputClient.
-  // Note: On Windows, the returned value is supposed to be DIP (Density
-  // Independent Pixel).
-  // TODO(ime): Have a clear spec whether the returned value is DIP or not.
-  // http://crbug.com/360334
+  // Ensure the caret is not in |rect|.  |rect| is the screen coordinates in
+  // DIP (Density Independent Pixel) and may extend beyond the bounds of this
+  // TextInputClient.
   virtual void EnsureCaretNotInRect(const gfx::Rect& rect) = 0;
 
   // Returns true if |command| is currently allowed to be executed.
   virtual bool IsTextEditCommandEnabled(TextEditCommand command) const = 0;
 
   // Execute |command| on the next key event. This allows a TextInputClient to
   // be informed of a platform-independent edit command that has been derived
   // from the key event currently being dispatched (but not yet sent to the
   // TextInputClient). The edit command will take into account any OS-specific,
   // or user-specified, keybindings that may be set up.
   virtual void SetTextEditCommandForNextKeyEvent(TextEditCommand command) = 0;
 };
 
 }  // namespace ui
 
 #endif  // UI_BASE_IME_TEXT_INPUT_CLIENT_H_