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 a266cd53dabce54cd6bf3b13a408a98db3824451..92eff024ae00f123714b2f64b04f4b294b5d548e 100644
--- a/base/trace_event/common/trace_event_common.h
+++ b/base/trace_event/common/trace_event_common.h
@@ -962,6 +962,20 @@
       TRACE_EVENT_PHASE_DELETE_OBJECT, category_group, name,         \
       TRACE_ID_DONT_MANGLE(id), TRACE_EVENT_FLAG_NONE)
 
+// Records entering and leaving trace event contexts. |category_group| and
+// |name| specify the context category and type. |context| is a
+// snapshotted context object id.
+#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 {                                                                      \
@@ -1025,6 +1039,8 @@
 #define TRACE_EVENT_PHASE_MEMORY_DUMP ('v')
 #define TRACE_EVENT_PHASE_MARK ('R')
 #define TRACE_EVENT_PHASE_CLOCK_SYNC ('c')
+#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))