Replace wstring with string16 in sandbox

sandbox/win/src/policy_low_level.h

Index: sandbox/win/src/policy_low_level.h
diff --git a/sandbox/win/src/policy_low_level.h b/sandbox/win/src/policy_low_level.h
index 025a133ec6aae40e1a97ff5b1765f3458a0c644f..ca8b36fd4092a2f32b27b2ef5e45c572b51fb22d 100644
--- a/sandbox/win/src/policy_low_level.h
+++ b/sandbox/win/src/policy_low_level.h
@@ -8,6 +8,7 @@
 #include <list>
 
 #include "base/basictypes.h"
+#include "base/strings/string16.h"
 #include "sandbox/win/src/ipc_tags.h"
 #include "sandbox/win/src/policy_engine_params.h"
 #include "sandbox/win/src/policy_engine_opcodes.h"
@@ -163,7 +164,7 @@ class PolicyRule {
   // in AddStringMatch.
   bool GenStringOpcode(RuleType rule_type, StringMatchOptions match_opts,
                        uint16 parameter, int state, bool last_call,
-                       int* skip_count, std::wstring* fragment);
+                       int* skip_count, base::string16* fragment);
 
   // Loop over all generated opcodes and copy them to increasing memory
   // addresses from opcode_start and copy the extra data (strings usually) into