Use array<uint8> rather than string to pass BroadcastChannel messages.

third_party/WebKit/Source/modules/broadcastchannel/BroadcastChannel.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 BroadcastChannel_h
 #define BroadcastChannel_h
 
 #include "bindings/core/v8/ActiveScriptWrappable.h"
 #include "core/dom/ContextLifecycleObserver.h"
 #include "core/events/EventTarget.h"
@@ skipping 32 matching lines @@
 
     // ContextLifecycleObserver:
     void contextDestroyed() override;
 
     DECLARE_VIRTUAL_TRACE();
 
 private:
     BroadcastChannel(ExecutionContext*, const String& name);
 
     // mojom::blink::BroadcastChannelClient:
-    void OnMessage(const String& message) override;
+    void OnMessage(mojo::WTFArray<uint8_t> message) override;
 
     // Called when the mojo binding disconnects.
     void onError();
 
     RefPtr<SecurityOrigin> m_origin;
     String m_name;
 
     mojo::AssociatedBinding<mojom::blink::BroadcastChannelClient> m_binding;
     mojom::blink::BroadcastChannelClientAssociatedPtr m_remoteClient;
 };
 
 } // namespace blink
 
 #endif // BroadcastChannel_h