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

base/trace_event/trace_event.h

 // Copyright (c) 2012 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.
 
 // This header file defines the set of trace_event macros without specifying
 // how the events actually get collected and stored. If you need to expose trace
 // events to some other universe, you can copy-and-paste this file as well as
 // trace_event.h, modifying the macros contained there as necessary for the
 // target platform. The end result is that multiple libraries can funnel events
 // through to a shared trace event collector.
@@ skipping 899 matching lines @@
 #define TRACE_EVENT_CATEGORY_GROUP_ENABLED(category_group, ret) \
     do { \
       INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group); \
       if (INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE()) { \
         *ret = true; \
       } else { \
         *ret = false; \
       } \
     } 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 { \
       static int INTERNAL_TRACE_EVENT_UID(lastRecordingNumber) = 0; \
       int num_traces_recorded = TRACE_EVENT_API_GET_NUM_TRACES_RECORDED(); \
       if (num_traces_recorded != -1 && \
           num_traces_recorded != \
           INTERNAL_TRACE_EVENT_UID(lastRecordingNumber)) { \
         INTERNAL_TRACE_EVENT_UID(lastRecordingNumber) = \
             num_traces_recorded; \
@@ skipping 816 matching lines @@
   const char* name_;
   IDType id_;
 
   DISALLOW_COPY_AND_ASSIGN(TraceScopedTrackableObject);
 };
 
 }  // namespace trace_event
 }  // namespace base
 
 #endif  // BASE_TRACE_EVENT_TRACE_EVENT_H_