Conservative update button/label/textfield content

ui/views/controls/label.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/label.h"
 
 #include <algorithm>
 #include <cmath>
 #include <limits>
 #include <vector>
@@ skipping 36 matching lines @@
 }
 
 void Label::SetFont(const gfx::Font& font) {
   font_ = font;
   text_size_valid_ = false;
   PreferredSizeChanged();
   SchedulePaint();
 }
 
 void Label::SetText(const string16& text) {
+  if (text == text_)
+    return;
   text_ = text;
   text_size_valid_ = false;
   is_email_ = false;
   PreferredSizeChanged();
   SchedulePaint();
 }
 
 void Label::SetEmail(const string16& email) {
   SetText(email);
   is_email_ = true;
@@ skipping 426 matching lines @@
                                 ui::ELIDE_AT_END);
   } else {
     *paint_text = text_;
   }
 
   *text_bounds = GetTextBounds();
   *flags = ComputeDrawStringFlags();
 }
 
 }  // namespace views