Switch the offset conversion routines from...

base/strings/utf_offset_string_conversions.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 BASE_STRINGS_UTF_OFFSET_STRING_CONVERSIONS_H_
 #define BASE_STRINGS_UTF_OFFSET_STRING_CONVERSIONS_H_
 
 #include <string>
 #include <vector>
 
 #include "base/base_export.h"
 #include "base/strings/string16.h"
 #include "base/strings/string_piece.h"
 
 namespace base {
 
 // Like the conversions in utf_string_conversions.h, but also takes one or more
-// offsets (|offset[s]_for_adjustment|) into the source strings, each offset
-// will be adjusted to point at the same logical place in the result strings.
-// If this isn't possible because an offset points past the end of the source
-// strings or into the middle of a multibyte sequence, the offending offset will
-// be set to string16::npos. |offset[s]_for_adjustment| may be NULL.
+// |offset[s]_for_adjustment| representing insertion/selection points between
+// characters: if |src| is "abcd", then 0 is before 'a', 2 is between 'b' and
+// 'c', and 4 is at the end of the string.  Valid input offsets range from 0 to
+// |src_len|.  On exit, each offset will have been modified to point at the same
+// logical position in the output string.  If an offset cannot be successfully
+// adjusted (e.g. because it points into the middle of a multibyte sequence), it
+// will be set to string16::npos.
+//
+// |offset[s]_for_adjustment| may be NULL.
 BASE_EXPORT bool UTF8ToUTF16AndAdjustOffset(const char* src,
                                             size_t src_len,
                                             string16* output,
                                             size_t* offset_for_adjustment);
 BASE_EXPORT bool UTF8ToUTF16AndAdjustOffsets(
     const char* src,
     size_t src_len,
     string16* output,
     std::vector<size_t>* offsets_for_adjustment);
 
 BASE_EXPORT string16 UTF8ToUTF16AndAdjustOffset(const base::StringPiece& utf8,
                                                 size_t* offset_for_adjustment);
 BASE_EXPORT string16 UTF8ToUTF16AndAdjustOffsets(
     const base::StringPiece& utf8,
     std::vector<size_t>* offsets_for_adjustment);
 
 BASE_EXPORT std::string UTF16ToUTF8AndAdjustOffset(
     const base::StringPiece16& utf16,
     size_t* offset_for_adjustment);
 BASE_EXPORT std::string UTF16ToUTF8AndAdjustOffsets(
     const base::StringPiece16& utf16,
     std::vector<size_t>* offsets_for_adjustment);
 
 // Limiting function callable by std::for_each which will replace any value
-// which is equal to or greater than |limit| with npos.
+// which is greater than |limit| with npos.  Typically this is called with a
+// string length to clamp offsets into the string to [0, length] (as opposed to
+// [0, length); see comments above).
 template <typename T>
 struct LimitOffset {
   explicit LimitOffset(size_t limit)
     : limit_(limit) {}
 
   void operator()(size_t& offset) {
-    if (offset >= limit_)
+    if (offset > limit_)
       offset = T::npos;
   }
 
   size_t limit_;
 };
 
 // Stack object which, on destruction, will update a vector of offsets based on
 // any supplied adjustments.  To use, declare one of these, providing the
 // address of the offset vector to adjust.  Then Add() any number of Adjustments
 // (each Adjustment gives the |original_offset| of a substring and the lengths
@@ skipping 19 matching lines @@
  private:
   void AdjustOffset(std::vector<size_t>::iterator offset);
 
   std::vector<size_t>* offsets_for_adjustment_;
   std::vector<Adjustment> adjustments_;
 };
 
 }  // namespace base
 
 #endif  // BASE_STRINGS_UTF_OFFSET_STRING_CONVERSIONS_H_