tracing: Add macros for generating context trace events

base/trace_event/common/trace_event_common.h

Index: base/trace_event/common/trace_event_common.h
diff --git a/base/trace_event/common/trace_event_common.h b/base/trace_event/common/trace_event_common.h
index 72202f3cc16e899e4f3843a66b9e1b80436ef2d8..e4d4c91f1cf446f107bdc4ef700767ef32c56766 100644
--- a/base/trace_event/common/trace_event_common.h
+++ b/base/trace_event/common/trace_event_common.h
@@ -951,6 +951,20 @@
       TRACE_EVENT_PHASE_DELETE_OBJECT, category_group, name,         \
       TRACE_ID_DONT_MANGLE(id), TRACE_EVENT_FLAG_NONE)
 
+// Entering and leaving trace event contexts. |category_group| and |name|
+// specify the context category and type. |context| represents a snapshotted
+// context object.
+#define TRACE_EVENT_ENTER_CONTEXT(category_group, name, context) \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                              \
+      TRACE_EVENT_PHASE_ENTER_CONTEXT, category_group, name,     \
+      TRACE_ID_DONT_MANGLE(context), TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_LEAVE_CONTEXT(category_group, name, context) \
+  INTERNAL_TRACE_EVENT_ADD_WITH_ID(                              \
+      TRACE_EVENT_PHASE_LEAVE_CONTEXT, category_group, name,     \
+      TRACE_ID_DONT_MANGLE(context), TRACE_EVENT_FLAG_NONE)
+#define TRACE_EVENT_SCOPED_CONTEXT(category_group, name, context) \
+  INTERNAL_TRACE_EVENT_SCOPED_CONTEXT(category_group, name, context)
+
 // Macro to efficiently determine if a given category group is enabled.
 #define TRACE_EVENT_CATEGORY_GROUP_ENABLED(category_group, ret)             \
   do {                                                                      \
@@ -1013,6 +1027,8 @@
 #define TRACE_EVENT_PHASE_DELETE_OBJECT ('D')
 #define TRACE_EVENT_PHASE_MEMORY_DUMP ('v')
 #define TRACE_EVENT_PHASE_MARK ('R')
+#define TRACE_EVENT_PHASE_ENTER_CONTEXT ('(')
+#define TRACE_EVENT_PHASE_LEAVE_CONTEXT (')')
 
 // Flags for changing the behavior of TRACE_EVENT_API_ADD_TRACE_EVENT.
 #define TRACE_EVENT_FLAG_NONE (static_cast<unsigned int>(0))