Simplify OriginTrialContext and the way it validates tokens.

content/common/origin_trials/trial_token_validator.h

Index: content/common/origin_trials/trial_token_validator.h
diff --git a/content/common/origin_trials/trial_token_validator.h b/content/common/origin_trials/trial_token_validator.h
index 07f99c745ff7db1c8464472f3eec039278e4f19d..ec74e9ac5ae26c3433eef76b2040e17681cb5a6e 100644
--- a/content/common/origin_trials/trial_token_validator.h
+++ b/content/common/origin_trials/trial_token_validator.h
@@ -18,11 +18,13 @@ 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