media: Always enable trace event for "media" category group.

base/trace_event/trace_event.h

Index: base/trace_event/trace_event.h
diff --git a/base/trace_event/trace_event.h b/base/trace_event/trace_event.h
index a2fb97c9932c3b0df7d8ff7db2eb29f1d7286c9e..962493774e8275209288807a7f856bb3277eb5c2 100644
--- a/base/trace_event/trace_event.h
+++ b/base/trace_event/trace_event.h
@@ -917,6 +917,14 @@
       } \
     } while (0)
 
+// Macro to explicitly warm up a given category group. This could be useful in
+// cases where we want to initialize a category group before any trace events
+// for that category group is reported. For example, to have a category group
+// always show up in the "record categories" list for manually selecting
+// settings in about://tracing.
+#define TRACE_EVENT_WARMUP_CATEGORY(category_group) \
+  INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group)
+
 // Macro to efficiently determine, through polling, if a new trace has begun.
 #define TRACE_EVENT_IS_NEW_TRACE(ret) \
     do { \