content: Cleanup class/struct forward declarations

content/public/browser/tracing_delegate.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 CONTENT_PUBLIC_BROWSER_TRACING_DELEGATE_H_
 #define CONTENT_PUBLIC_BROWSER_TRACING_DELEGATE_H_
 
 #include <memory>
 #include <string>
 
 #include "base/callback.h"
 #include "content/common/content_export.h"
 
 namespace base {
 class DictionaryValue;
-class Time;
 }
 
 namespace net {
 class URLRequestContextGetter;
 }
 
 namespace content {
 class BackgroundTracingConfig;
 class TraceUploader;
 
@@ skipping 21 matching lines @@
 
   // Used to add any additional metadata to traces.
   virtual void GenerateMetadataDict(base::DictionaryValue* metadata_dict) {}
 
   virtual MetadataFilterPredicate GetMetadataFilterPredicate();
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_TRACING_DELEGATE_H_