Use base::string16 for CompositionText.Text instead of converting to utf-8 and back unnecessarily.

ui/base/ime/input_method_chromeos.cc

 // Copyright 2014 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/base/ime/input_method_chromeos.h"
 
 #include <algorithm>
 #include <cstring>
 #include <set>
 #include <vector>
@@ skipping 478 matching lines @@
     const chromeos::CompositionText& text,
     uint32 cursor_pos,
     bool visible) {
   if (IsTextInputTypeNone())
     return;
 
   if (!CanComposeInline()) {
     chromeos::IBusPanelCandidateWindowHandlerInterface* candidate_window =
         chromeos::IMEBridge::Get()->GetCandidateWindowHandler();
     if (candidate_window)
-      candidate_window->UpdatePreeditText(
-          base::UTF8ToUTF16(text.text()), cursor_pos, visible);
+      candidate_window->UpdatePreeditText(text.text(), cursor_pos, visible);
   }
 
   // |visible| argument is very confusing. For example, what's the correct
   // behavior when:
   // 1. OnUpdatePreeditText() is called with a text and visible == false, then
   // 2. OnShowPreeditText() is called afterwards.
   //
   // If it's only for clearing the current preedit text, then why not just use
   // OnHidePreeditText()?
   if (!visible) {
@@ skipping 42 matching lines @@
   if (GetTextInputClient())
     GetTextInputClient()->ExtendSelectionAndDelete(length, 0U);
 }
 
 bool InputMethodChromeOS::ExecuteCharacterComposer(const ui::KeyEvent& event) {
   if (!character_composer_.FilterKeyPress(event))
     return false;
 
   // CharacterComposer consumed the key event.  Update the composition text.
   chromeos::CompositionText preedit;
-  preedit.set_text(
-      base::UTF16ToUTF8(character_composer_.preedit_string()));
+  preedit.set_text(character_composer_.preedit_string());
   UpdateCompositionText(preedit, preedit.text().size(),
                         !preedit.text().empty());
   std::string commit_text =
       base::UTF16ToUTF8(character_composer_.composed_character());
   if (!commit_text.empty()) {
     CommitText(commit_text);
   }
   return true;
 }
 
 void InputMethodChromeOS::ExtractCompositionText(
     const chromeos::CompositionText& text,
     uint32 cursor_position,
     CompositionText* out_composition) const {
   out_composition->Clear();
-  out_composition->text = base::UTF8ToUTF16(text.text());
+  out_composition->text = text.text();
 
   if (out_composition->text.empty())
     return;
 
   // ibus uses character index for cursor position and attribute range, but we
   // use char16 offset for them. So we need to do conversion here.
   std::vector<size_t> char16_offsets;
   size_t length = out_composition->text.length();
   base::i18n::UTF16CharIterator char_iterator(&out_composition->text);
   do {
@@ skipping 53 matching lines @@
   }
 
   // Use a black thin underline by default.
   if (out_composition->underlines.empty()) {
     out_composition->underlines.push_back(CompositionUnderline(
         0, length, SK_ColorBLACK, false /* thick */));
   }
 }
 
 }  // namespace ui