Stop combining text runs which are connected by 'COMMON' blocks.

ui/gfx/render_text_harfbuzz.h

Index: ui/gfx/render_text_harfbuzz.h
diff --git a/ui/gfx/render_text_harfbuzz.h b/ui/gfx/render_text_harfbuzz.h
index 6d8fa8d962a13e7067e0d2f759cf8f9dbdb89916..6b09dbb81ff5c195492d9c9831d22dc8cb70cae8 100644
--- a/ui/gfx/render_text_harfbuzz.h
+++ b/ui/gfx/render_text_harfbuzz.h
@@ -115,6 +115,9 @@ class TextRunList {
   // Do not use this when multiline is enabled.
   float width() const { return width_; }
 
+  // Get the run index applicable to |position| (at or preceeding |position|).
+  size_t GetRunIndexAt(size_t position) const;
+
  private:
   // Text runs in logical order.
   ScopedVector<TextRunHarfBuzz> runs_;
@@ -165,6 +168,7 @@ class GFX_EXPORT RenderTextHarfBuzz : public RenderText {
 
  private:
   friend class RenderTextTest;
+  FRIEND_TEST_ALL_PREFIXES(RenderTextTest, Multiline_LineBreakerBehavior);
   FRIEND_TEST_ALL_PREFIXES(RenderTextTest, Multiline_HorizontalAlignment);
   FRIEND_TEST_ALL_PREFIXES(RenderTextTest, Multiline_NormalWidth);
   FRIEND_TEST_ALL_PREFIXES(RenderTextTest, Multiline_WordWrapBehavior);