Add UTF16ToUTF8AndAdjustOffset() to base/.

base/utf_offset_string_conversions.h

Index: base/utf_offset_string_conversions.h
diff --git a/base/utf_offset_string_conversions.h b/base/utf_offset_string_conversions.h
index 01177b655dc2d1d94139c1cdfdd8be94dd6c33b8..c2faf3a491599cf33648d06380fd8525876d7868 100644
--- a/base/utf_offset_string_conversions.h
+++ b/base/utf_offset_string_conversions.h
@@ -14,6 +14,7 @@
 
 namespace base {
 class StringPiece;
+class StringPiece16;
 }
 
 // Like the conversions in utf_string_conversions.h, but also takes one or more
@@ -38,6 +39,13 @@ 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.
 template <typename T>