Don't split text runs on underline style change

ui/gfx/render_text.cc

Index: ui/gfx/render_text.cc
diff --git a/ui/gfx/render_text.cc b/ui/gfx/render_text.cc
index fe4c59cee9b3239dd18b982628203b55a885b9f6..e0da64d683c69c3b966b54340d8a809be46fdc04 100644
--- a/ui/gfx/render_text.cc
+++ b/ui/gfx/render_text.cc
@@ -651,7 +651,10 @@ void RenderText::SetStyle(TextStyle style, bool value) {
 }
 
 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();