tracing: simplify lifetime of TraceEventFilter(s)

base/trace_event/trace_event_filter.h

Index: base/trace_event/trace_event_filter.h
diff --git a/base/trace_event/trace_event_filter.h b/base/trace_event/trace_event_filter.h
index 48c6711432fdadc013b3b6ca5be668d42337e98e..a23c6a2a96e30209f0c6509d7e961a1099bf7712 100644
--- a/base/trace_event/trace_event_filter.h
+++ b/base/trace_event/trace_event_filter.h
@@ -29,7 +29,15 @@ class TraceEvent;
 // different threads.
 class BASE_EXPORT TraceEventFilter {
  public:
-  TraceEventFilter();
+  // Basic configuration shared by all filters.
+  class Config {
+   public:
+    Config();
+    virtual ~Config();
+    virtual bool IsEnabledForCategory(const char* category_name) const = 0;
+  };
+
+  explicit TraceEventFilter(std::unique_ptr<Config>);
   virtual ~TraceEventFilter();
 
   // If the category is ENABLED_FOR_RECORDING, the event is added iff all the
@@ -41,7 +49,11 @@ class BASE_EXPORT TraceEventFilter {
   virtual void EndEvent(const char* category_name,
                         const char* event_name) const;
 
+  bool IsEnabledForCategory(const char* category_name) const;
+
  private:
+  std::unique_ptr<const Config> config_;
+
   DISALLOW_COPY_AND_ASSIGN(TraceEventFilter);
 };