Move more uses of string16 to specify base::

ui/gfx/utf16_indexing.h

Index: ui/gfx/utf16_indexing.h
diff --git a/ui/gfx/utf16_indexing.h b/ui/gfx/utf16_indexing.h
index a9eaea2dd9aaedceb7b9ecd554bb407b455af481..4c2b2c19d562fb0b0cc953865db0158604559494 100644
--- a/ui/gfx/utf16_indexing.h
+++ b/ui/gfx/utf16_indexing.h
@@ -12,7 +12,7 @@ namespace gfx {
 
 // Returns false if s[index-1] is a high surrogate and s[index] is a low
 // surrogate, true otherwise.
-GFX_EXPORT bool IsValidCodePointIndex(const string16& s, size_t index);
+GFX_EXPORT bool IsValidCodePointIndex(const base::string16& s, size_t index);
 
 // |UTF16IndexToOffset| returns the number of code points between |base| and
 // |pos| in the given string. |UTF16OffsetToIndex| returns the index that is
@@ -37,10 +37,10 @@ GFX_EXPORT bool IsValidCodePointIndex(const string16& s, size_t index);
 //   Always,
 //     UTF16IndexToOffset(s, base, UTF16OffsetToIndex(s, base, ofs)) == ofs
 //     UTF16IndexToOffset(s, i, j) == -UTF16IndexToOffset(s, j, i)
-GFX_EXPORT ptrdiff_t UTF16IndexToOffset(const string16& s,
+GFX_EXPORT ptrdiff_t UTF16IndexToOffset(const base::string16& s,
                                         size_t base,
                                         size_t pos);
-GFX_EXPORT size_t UTF16OffsetToIndex(const string16& s,
+GFX_EXPORT size_t UTF16OffsetToIndex(const base::string16& s,
                                      size_t base,
                                      ptrdiff_t offset);