[Tracing] Add metadata filter

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 <string>
+
+#include "base/callback.h"
 #include "base/memory/scoped_ptr.h"
 #include "content/common/content_export.h"
 
 namespace base {
 class DictionaryValue;
 class Time;
 }
 
 namespace net {
 class URLRequestContextGetter;
 }
 
 namespace content {
 class BackgroundTracingConfig;
 class TraceUploader;
 
+typedef base::Callback<bool(const std::string& metadata_name)>
+    MetadataFilterPredicate;
+
 // This can be implemented by the embedder to provide functionality for the
 // about://tracing WebUI.
 class CONTENT_EXPORT TracingDelegate {
  public:
   virtual ~TracingDelegate() {}
 
   // Provide trace uploading functionality; see trace_uploader.h.
   virtual scoped_ptr<TraceUploader> GetTraceUploader(
       net::URLRequestContextGetter* request_context) = 0;
 
   // This can be used to veto a particular background tracing scenario.
   virtual bool IsAllowedToBeginBackgroundScenario(
       const BackgroundTracingConfig& config,
       bool requires_anonymized_data);
 
   virtual bool IsAllowedToEndBackgroundScenario(
       const content::BackgroundTracingConfig& config,
       bool requires_anonymized_data);
 
   // 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_