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

ui/base/ime/text_input_client.h

Index: ui/base/ime/text_input_client.h
diff --git a/ui/base/ime/text_input_client.h b/ui/base/ime/text_input_client.h
index d76c00a49a9681f9f2171a652549ef75eeeed778..c84d3bdb2b565a63c36c50b487ac8d099c13e3ba 100644
--- a/ui/base/ime/text_input_client.h
+++ b/ui/base/ime/text_input_client.h
@@ -81,24 +81,23 @@ class UI_BASE_IME_EXPORT TextInputClient {
   // 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;
 
@@ -162,12 +161,9 @@ class UI_BASE_IME_EXPORT TextInputClient {
   // 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.