Improve RenderTextWin font fallback.

ui/gfx/render_text.h

Index: ui/gfx/render_text.h
===================================================================
--- ui/gfx/render_text.h	(revision 111944)
+++ ui/gfx/render_text.h	(working copy)
@@ -209,7 +209,7 @@
   virtual SelectionModel LeftEndSelectionModel();
   virtual SelectionModel RightEndSelectionModel();
 
-  // Get the logical index of the grapheme preceeding the argument |position|.
+  // Get the logical index of the grapheme preceding the argument |position|.
   virtual size_t GetIndexOfPreviousGrapheme(size_t position);
 
   // Get the visual bounds containing the logical substring within |from| to
@@ -220,9 +220,12 @@
   // TODO(msw) Re-evaluate this function's necessity and signature.
   virtual std::vector<Rect> GetSubstringBounds(size_t from, size_t to);
 
-  // Return true if cursor can appear in front of the character at |position|,
-  // which means it is a grapheme boundary or the first character in the text.
-  virtual bool IsCursorablePosition(size_t position) = 0;
+  // Returns true if the cursor can appear at the specified location, which
+  // means it is a grapheme boundary or the first character in the text. If
+  // |is_trailing| is false, the location specified is in front of the character
+  // at index |position|, otherwise the location corresponds to the end of the
+  // character.
+  virtual bool IsCursorablePosition(size_t position, bool is_trailing) = 0;

[msw, 2011/11/29 20:42:00]

Can this take a SelectionModel::CaretPlacement instead of a bool?

 
   // Updates the layout so that the next draw request can correctly
   // render the text and its attributes.