[Tracing] Add metadata filter

content/public/browser/tracing_delegate.cc

 // 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.
 
 #include "content/public/browser/tracing_delegate.h"
 
 namespace content {
 
 bool TracingDelegate::IsAllowedToBeginBackgroundScenario(
     const BackgroundTracingConfig& config,
     bool requires_anonymized_data) {
   return false;
 }
 
 bool TracingDelegate::IsAllowedToEndBackgroundScenario(
     const content::BackgroundTracingConfig& config,
     bool requires_anonymized_data) {
   return false;
 }
 
+MetadataFilterPredicate TracingDelegate::GetMetadataFilterPredicate() {
+  return MetadataFilterPredicate();
+}
+
 }  // namespace content