Improve RenderTextWin font fallback.

ui/gfx/render_text.h

 // Copyright (c) 2011 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.
 
 #ifndef UI_GFX_RENDER_TEXT_H_
 #define UI_GFX_RENDER_TEXT_H_
 #pragma once
 
 #include <algorithm>
 #include <vector>
@@ skipping 191 matching lines @@
   virtual SelectionModel GetLeftSelectionModel(const SelectionModel& current,
                                                BreakType break_type);
   virtual SelectionModel GetRightSelectionModel(const SelectionModel& current,
                                                 BreakType break_type);
 
   // Get the SelectionModels corresponding to visual text ends.
   // The returned value represents a cursor/caret position without a selection.
   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
   // |to|. These bounds could be visually discontinuous if the substring is
   // split by a LTR/RTL level change. These bounds are in local coordinates, but
   // may be outside the visible region if the text is longer than the textfield.
   // Subsequent text, cursor, or bounds changes may invalidate returned values.
   // 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.
   virtual void UpdateLayout() = 0;
 
   // Apply composition style (underline) to composition range and selection
   // style (foreground) to selection range.
   void ApplyCompositionAndSelectionStyles(StyleRanges* style_ranges) const;
 
   // Convert points from the text space to the view space and back.
@@ skipping 60 matching lines @@
   // The cached bounds and offset are invalidated by changes to the cursor,
   // selection, font, and other operations that adjust the visible text bounds.
   bool cached_bounds_and_offset_valid_;
 
   DISALLOW_COPY_AND_ASSIGN(RenderText);
 };
 
 }  // namespace gfx
 
 #endif  // UI_GFX_RENDER_TEXT_H_