fix know issues in RenderText

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 175 matching lines @@
 
   // Moves the cursor left or right. Cursor movement is visual, meaning that
   // left and right are relative to screen, not the directionality of the text.
   // If |select| is false, the selection start is moved to the same position.
   void MoveCursorLeft(BreakType break_type, bool select);
   void MoveCursorRight(BreakType break_type, bool select);
 
   // Set the selection_model_ to the value of |selection|.
   // The selection model components are modified if invalid.
   // Returns true if the cursor position or selection range changed.
-  // TODO(xji): need to check the cursor is set at grapheme boundary.
+  // If |selectin_start_| or |selection_end_| or |caret_pos_| in
+  // |selection_model| is not a cursorable position (not on grapheme boundary),
+  // it is a NO-OP and returns false.
   bool MoveCursorTo(const SelectionModel& selection_model);
 
   // Move the cursor to the position associated with the clicked point.
   // If |select| is false, the selection start is moved to the same position.
   // Returns true if the cursor position or selection range changed.
   bool MoveCursorTo(const Point& point, bool select);
 
   size_t GetSelectionStart() const {
       return selection_model_.selection_start();
   }
@@ skipping 40 matching lines @@
   // may be outside the visible region if the text is longer than the textfield.
   // Subsequent text, cursor, or bounds changes may invalidate returned values.
   virtual Rect GetCursorBounds(const SelectionModel& selection,
                                bool insert_mode);
 
   // Compute the current cursor bounds, panning the text to show the cursor in
   // the display rect if necessary. These bounds are in local coordinates.
   // Subsequent text, cursor, or bounds changes may invalidate returned values.
   const Rect& GetUpdatedCursorBounds();
 
+  // Get the logical index of the grapheme following the argument |position|.
+  virtual size_t GetIndexOfNextGrapheme(size_t position);
+
  protected:
   RenderText();
 
   const Point& GetUpdatedDisplayOffset();
 
   void set_cached_bounds_and_offset_valid(bool valid) {
       cached_bounds_and_offset_valid_ = valid;
   }
 
   const StyleRanges& style_ranges() const { return style_ranges_; }
@@ skipping 14 matching lines @@
   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;
+
   // 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.
   // Handles the display area, display offset, and the application LTR/RTL mode.
   Point ToTextPoint(const Point& point);
   Point ToViewPoint(const Point& point);
 
  private:
   friend class RenderTextTest;
 
   FRIEND_TEST_ALL_PREFIXES(RenderTextTest, DefaultStyle);
   FRIEND_TEST_ALL_PREFIXES(RenderTextTest, CustomDefaultStyle);
   FRIEND_TEST_ALL_PREFIXES(RenderTextTest, ApplyStyleRange);
   FRIEND_TEST_ALL_PREFIXES(RenderTextTest, StyleRangesAdjust);
 
+  // Return an index belonging to the |next| or previous logical grapheme.
+  // The return value is bounded by 0 and the text length, inclusive.
+  virtual size_t IndexOfAdjacentGrapheme(size_t index, bool next) = 0;
+
   // Sets the selection model, the argument is assumed to be valid.
   void SetSelectionModel(const SelectionModel& selection_model);
 
   // Set the cursor to |position|, with the caret trailing the previous
   // grapheme, or if there is no previous grapheme, leading the cursor position.
   // If |select| is false, the selection start is moved to the same position.
+  // If the |position| is not a cursorable position (not on grapheme boundary),
+  // it is a NO-OP.
   void MoveCursorTo(size_t position, bool select);
 
-  bool IsPositionAtWordSelectionBoundary(size_t pos);
-
   // Update the cached bounds and display offset to ensure that the current
   // cursor is within the visible display area.
   void UpdateCachedBoundsAndOffset();
 
   // Returns the selection model of selection_start_.
   // The returned value represents a cursor/caret position without a selection.
   SelectionModel GetSelectionModelForSelectionStart();
 
   // Logical UTF-16 string data to be drawn.
   string16 text_;
@@ skipping 28 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_