Simplify OriginTrialContext and the way it validates tokens.

content/common/origin_trials/trial_token_validator.h

 // Copyright 2016 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 CONTENT_COMMON_ORIGIN_TRIALS_TRIAL_TOKEN_VALIDATOR_H_
 #define CONTENT_COMMON_ORIGIN_TRIALS_TRIAL_TOKEN_VALIDATOR_H_
 
 #include <string>
 #include "base/strings/string_piece.h"
 #include "content/common/content_export.h"
 #include "url/origin.h"
 
 namespace blink {
 enum class WebOriginTrialTokenStatus;
 }
 
 namespace content {
 
 namespace TrialTokenValidator {
 
+// If token validates, |*feature_name| is set to the name of the feature the
+// token enables.
 // This method is thread-safe.
 CONTENT_EXPORT blink::WebOriginTrialTokenStatus ValidateToken(
     const std::string& token,
     const url::Origin& origin,
-    base::StringPiece feature_name);
+    std::string* feature_name);
 
 }  // namespace TrialTokenValidator
 
 }  // namespace content
 
 #endif  // CONTENT_COMMON_ORIGIN_TRIALS_TRIAL_TOKEN_VALIDATOR_H_