tracing: Add macros for generating context trace events

third_party/WebKit/Source/platform/TraceEvent.h

 /*
  * Copyright (C) 2011 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1.  Redistributions of source code must retain the above copyright
  *     notice, this list of conditions and the following disclaimer.
  * 2.  Redistributions in binary form must reproduce the above copyright
@@ skipping 216 matching lines @@
     do { \
         INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category); \
         if (INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE()) { \
             blink::TraceEvent::addTraceEvent( \
                 phase, INTERNALTRACEEVENTUID(categoryGroupEnabled), name, \
                 blink::TraceEvent::noEventId, blink::TraceEvent::noBindId, \
                 timestamp, flags, ##__VA_ARGS__); \
         } \
     } while (0)
 
+// Implementation detail: internal macro to enter and leave a context based on
+// the current scope.
+#define INTERNAL_TRACE_EVENT_SCOPED_CONTEXT(categoryGroup, name, context) \
+    blink::TraceEvent::TraceScopedContext INTERNAL_TRACE_EVENT_UID(scopedTracer)(categoryGroup, name, context)
 
 // These values must be in sync with base::debug::TraceLog::CategoryGroupEnabledFlags.
 #define ENABLED_FOR_RECORDING (1 << 0)
 #define ENABLED_FOR_EVENT_CALLBACK (1 << 2)
 
 #define INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE() \
     (*INTERNALTRACEEVENTUID(categoryGroupEnabled) & (ENABLED_FOR_RECORDING | ENABLED_FOR_EVENT_CALLBACK))
 
 #define INTERNAL_TRACE_MEMORY(category, name)
 
@@ skipping 359 matching lines @@
     {
         TRACE_EVENT_OBJECT_DELETED_WITH_ID(m_categoryGroup, m_name, m_id);
     }
 
 private:
     const char* m_categoryGroup;
     const char* m_name;
     IDType m_id;
 };
 
+using TraceContext = const void*;
+
+class TraceScopedContext {
+    WTF_MAKE_NONCOPYABLE(TraceScopedContext);
+
+public:
+    TraceScopedContext(const char* categoryGroup, const char* name, TraceContext context)
+        : m_categoryGroup(categoryGroup)
+        , m_name(name)
+        , m_context(context)
+    {
+        TRACE_EVENT_ENTER_CONTEXT(m_categoryGroup, m_name, m_context);
+    }
+
+    ~TraceScopedContext()
+    {
+        TRACE_EVENT_LEAVE_CONTEXT(m_categoryGroup, m_name, m_context);
+    }
+
+private:
+    const char* m_categoryGroup;
+    const char* m_name;
+    TraceContext m_context;
+};
+
 } // namespace TraceEvent
 
 } // namespace blink
 
 #endif