Avoid unnecessary wtf/text/WTFString.h includes in platform/heap/

third_party/WebKit/Source/modules/audio_output_devices/SetSinkIdCallbacks.h

 // Copyright 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 SetSinkIdCallbacks_h
 #define SetSinkIdCallbacks_h
 
 #include "platform/Timer.h"
 #include "platform/heap/Handle.h"
 #include "public/platform/WebSetSinkIdCallbacks.h"
 #include "wtf/Noncopyable.h"
 #include "wtf/RefPtr.h"
+#include "wtf/text/WTFString.h"
 
 namespace blink {
 
 class HTMLMediaElement;
 class ScriptPromiseResolver;
 
 class SetSinkIdCallbacks final : public WebSetSinkIdCallbacks {
     // FIXME(tasak): when making public/platform classes to use PartitionAlloc,
     // the following macro should be moved to WebCallbacks defined in public/platformWebCallbacks.h.
     USING_FAST_MALLOC(SetSinkIdCallbacks);
     WTF_MAKE_NONCOPYABLE(SetSinkIdCallbacks);
 public:
     SetSinkIdCallbacks(ScriptPromiseResolver*, HTMLMediaElement&, const String& sinkId);
     ~SetSinkIdCallbacks() override;
 
     void onSuccess() override;
     void onError(WebSetSinkIdError) override;
 
 private:
     Persistent<ScriptPromiseResolver> m_resolver;
     RefPtrWillBePersistent<HTMLMediaElement> m_element;
     String m_sinkId;
 };
 
 } // namespace blink
 
 #endif // SetSinkIdCallbacks_h