WebRTCCertificateGenerator should not use std::string.

content/renderer/media/rtc_certificate_generator.h

 // Copyright (c) 2015 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_RENDERER_MEDIA_RTC_CERTIFICATE_GENERATOR_H_
 #define CONTENT_RENDERER_MEDIA_RTC_CERTIFICATE_GENERATOR_H_
 
 #include "base/macros.h"
 #include "third_party/WebKit/public/platform/WebRTCCertificate.h"
 #include "third_party/WebKit/public/platform/WebRTCCertificateGenerator.h"
@@ skipping 13 matching lines @@
   // blink::WebRTCCertificateGenerator implementation.
   void generateCertificate(
       const blink::WebRTCKeyParams& key_params,
       std::unique_ptr<blink::WebRTCCertificateCallback> observer) override;
   void generateCertificateWithExpiration(
       const blink::WebRTCKeyParams& key_params,
       uint64_t expires_ms,
       std::unique_ptr<blink::WebRTCCertificateCallback> observer) override;
   bool isSupportedKeyParams(const blink::WebRTCKeyParams& key_params) override;
   std::unique_ptr<blink::WebRTCCertificate> fromPEM(
-      const std::string& pem_private_key,
-      const std::string& pem_certificate) override;
+      blink::WebString pem_private_key,
+      blink::WebString pem_certificate) override;
 
  private:
   void generateCertificateWithOptionalExpiration(
       const blink::WebRTCKeyParams& key_params,
       const rtc::Optional<uint64_t>& expires_ms,
       std::unique_ptr<blink::WebRTCCertificateCallback> observer);
 
   DISALLOW_COPY_AND_ASSIGN(RTCCertificateGenerator);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_RENDERER_MEDIA_RTC_CERTIFICATE_GENERATOR_H_