[Tracing] Add metadata filter

content/public/browser/tracing_delegate.h

Index: content/public/browser/tracing_delegate.h
diff --git a/content/public/browser/tracing_delegate.h b/content/public/browser/tracing_delegate.h
index e72e71b23565fd3043a584231fd9638708b26f8b..8b9a224ef7237b6ac5a6386b1dcd1aec1452041d 100644
--- a/content/public/browser/tracing_delegate.h
+++ b/content/public/browser/tracing_delegate.h
@@ -5,6 +5,9 @@
 #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"
 
@@ -21,6 +24,9 @@ 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 {
@@ -42,6 +48,8 @@ class CONTENT_EXPORT TracingDelegate {
 
   // Used to add any additional metadata to traces.
   virtual void GenerateMetadataDict(base::DictionaryValue* metadata_dict) {}
+
+  virtual MetadataFilterPredicate GetMetadataFilterPredicate();
 };
 
 }  // namespace content