[LayoutNG] Implement LayoutBR/preserved newlines and tabs

third_party/WebKit/Source/platform/fonts/Font.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2006, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (c) 2007, 2008, 2010 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 479 matching lines @@
   CachingWordShaper shaper(*this);
   auto ranges = shaper.IndividualCharacterRanges(run);
   // The shaper should return ranges.size == run.length but on some platforms
   // (OSX10.9.5) we are seeing cases in the upper end of the unicode range
   // where this is not true (see: crbug.com/620952). To catch these cases on
   // more popular platforms, and to protect users, we are using a CHECK here.
   CHECK_EQ(ranges.size(), run.length());
   return ranges;
 }
 
+LayoutUnit Font::TabWidth(const TabSize& tab_size, LayoutUnit position) const {
+  const SimpleFontData* font_data = PrimaryFont();
+  if (!font_data)
+    return LayoutUnit::FromFloatCeil(GetFontDescription().LetterSpacing());
+  float base_tab_width = tab_size.GetPixelSize(font_data->SpaceWidth());
+  if (!base_tab_width)
+    return LayoutUnit::FromFloatCeil(GetFontDescription().LetterSpacing());
+
+  LayoutUnit distance_to_tab_stop = LayoutUnit::FromFloatFloor(
+      base_tab_width - fmodf(position, base_tab_width));
+
+  // Let the minimum width be the half of the space width so that it's always
+  // recognizable.  if the distance to the next tab stop is less than that,
+  // advance an additional tab stop.
+  if (distance_to_tab_stop < font_data->SpaceWidth() / 2)
+    distance_to_tab_stop += base_tab_width;
+
+  return distance_to_tab_stop;
+}
+
 bool Font::LoadingCustomFonts() const {
   return font_fallback_list_ && font_fallback_list_->LoadingCustomFonts();
 }
 
 bool Font::IsFallbackValid() const {
   return !font_fallback_list_ || font_fallback_list_->IsValid();
 }
 
 }  // namespace blink