Move string_piece.h to base/strings.

base/strings/string_piece.h

Index: base/strings/string_piece.h
diff --git a/base/string_piece.h b/base/strings/string_piece.h
similarity index 99%
copy from base/string_piece.h
copy to base/strings/string_piece.h
index 416fca80cd1e7814a8b762b1913dded53b0a3754..13ca009c20290f3dafc24d9461de41c80a0817ae 100644
--- a/base/string_piece.h
+++ b/base/strings/string_piece.h
@@ -20,8 +20,8 @@
 // functions (find, find_first_of, etc.) are found to be useful in this context.
 //
 
-#ifndef BASE_STRING_PIECE_H_
-#define BASE_STRING_PIECE_H_
+#ifndef BASE_STRINGS_STRING_PIECE_H_
+#define BASE_STRINGS_STRING_PIECE_H_
 
 #include <stddef.h>
 
@@ -448,4 +448,4 @@ inline size_t hash_value(const base::StringPiece16& sp16) {
 
 }  // namespace BASE_HASH_NAMESPACE
 
-#endif  // BASE_STRING_PIECE_H_
+#endif  // BASE_STRINGS_STRING_PIECE_H_