Add more out of line copy ctors for complex classes.

ui/base/ime/composition_text.cc

 // Copyright (c) 2011 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/composition_text.h"
 
 namespace ui {
 
 CompositionText::CompositionText() {
 }
 
+CompositionText::CompositionText(const CompositionText& other) = default;
+
 CompositionText::~CompositionText() {
 }
 
 void CompositionText::Clear() {
   text.clear();
   underlines.clear();
   selection = gfx::Range();
 }
 
 void CompositionText::CopyFrom(const CompositionText& obj) {
   Clear();
   text = obj.text;
   for (size_t i = 0; i < obj.underlines.size(); i++) {
     underlines.push_back(obj.underlines[i]);
   }
   selection = obj.selection;
 }
 
 }  // namespace ui