Don't split text runs on underline style change

ui/gfx/render_text.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/gfx/render_text.h"
 
 #include <algorithm>
 #include <climits>
 
 #include "base/command_line.h"
@@ skipping 633 matching lines @@
 }
 
 void RenderText::SetStyle(TextStyle style, bool value) {
   styles_[style].SetValue(value);
 
   cached_bounds_and_offset_valid_ = false;
   ResetLayout();
 }
 
 void RenderText::ApplyStyle(TextStyle style, bool value, const Range& range) {
-  styles_[style].ApplyValue(value, range);
+  // Don't change style in the middle of grapheme to avoid breaking of ligature.

[msw, 2014/09/03 19:17:32]

nit: "Do not change styles mid-grapheme to avoid breaking ligatures."

+  const size_t corrected_end =

[msw, 2014/09/03 19:17:32]

We should only correct the range bounds as needed:
  size_t end = IsValidCursorIndex(range.end()) ? range.end() :
      IndexOfAdjacentGrapheme(range.end(), CURSOR_FORWARD);

+      IndexOfAdjacentGrapheme(range.end() - 1, CURSOR_FORWARD);
+  styles_[style].ApplyValue(value, Range(range.start(), corrected_end));

[msw, 2014/09/03 19:17:32]

We should also correct the range start (using CURSOR_BACKWARD).

 
   cached_bounds_and_offset_valid_ = false;
   ResetLayout();
 }
 
 bool RenderText::GetStyle(TextStyle style) const {
   return (styles_[style].breaks().size() == 1) &&
       styles_[style].breaks().front().second;
 }
 
@@ skipping 703 matching lines @@
   SetDisplayOffset(display_offset_.x() + delta_x);
 }
 
 void RenderText::DrawSelection(Canvas* canvas) {
   const std::vector<Rect> sel = GetSubstringBounds(selection());
   for (std::vector<Rect>::const_iterator i = sel.begin(); i < sel.end(); ++i)
     canvas->FillRect(*i, selection_background_focused_color_);
 }
 
 }  // namespace gfx