Implement right-to-left text rendering in Pepper.

ppapi/api/trusted/ppb_browser_font_trusted.idl

 /* Copyright (c) 2012 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.
  */
 
 /**
  * This file defines the <code>PPB_BrowserFont_Trusted</code> interface.
  */
 label Chrome {
   M19 = 1.0
@@ skipping 219 matching lines @@
    */
   int32_t MeasureText(
       [in] PP_Resource font,
       [in] PP_BrowserFont_Trusted_TextRun text);
 
   /**
    * Returns the character at the given pixel X position from the beginning of
    * the string. This handles complex scripts such as Arabic, where characters
    * may be combined or replaced depending on the context. Returns (uint32)-1
    * on failure.
+   *
+   * TODO(brettw) this function may be broken. See the CharPosRTL test. It
+   * seems to tell you "insertion point" rather than painting position. This
+   * is useful but maybe not what we intended here.
    */
   uint32_t CharacterOffsetForPixel(
       [in] PP_Resource font,
       [in] PP_BrowserFont_Trusted_TextRun text,
       [in] int32_t pixel_position);
 
   /**
    * Returns the horizontal advance to the given character if the string was
    * placed at the given position. This handles complex scripts such as Arabic,
    * where characters may be combined or replaced depending on context. Returns
    * -1 on error.
    */
   int32_t PixelOffsetForCharacter(
       [in] PP_Resource font,
       [in] PP_BrowserFont_Trusted_TextRun text,
       [in] uint32_t char_offset);
 };