Add NESTABLE_ASYNC APIs to Tracing

base/debug/trace_event.h

Index: base/debug/trace_event.h
diff --git a/base/debug/trace_event.h b/base/debug/trace_event.h
index f9dc1c94d6d65b885772a4b1bf3b16005c58c2e9..db78f74414e0e667d8cea2cf1c40eb257668806a 100644
--- a/base/debug/trace_event.h
+++ b/base/debug/trace_event.h
@@ -510,7 +510,9 @@
         value1_name, static_cast<int>(value1_val), \
         value2_name, static_cast<int>(value2_val))
 
-
+// ASYNC_STEP_* APIs should be only used by legacy code. New code should
+// consider using NESTABLE_ASYNC_* APIs to describe substeps within an async
+// event.
 // Records a single ASYNC_BEGIN event called "name" immediately, with 0, 1 or 2
 // associated arguments. If the category is not enabled, then this
 // does nothing.
@@ -634,6 +636,45 @@
         static_cast<int>(base::PlatformThread::CurrentId()), \
         timestamp, TRACE_EVENT_FLAG_NONE)
 
+// NESTABLE_ASYNC_* APIs are used to describe an async operation, which can
+// be nested within a NESTABLE_ASYNC event and/or have inner NESTABLE_ASYNC
+// events.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+// - |id| is used to match the NESTABLE_ASYNC_BEGIN event with the
+//   NESTABLE_ASYNC_END event. Events are considered to match if their
+//   category_group, name and id values all match. |id| must either be a
+//   pointer or an integer value up to 64 bits. If it's a pointer, the bits
+//   will be xored with a hash of the process ID so that the same pointer on two
+//   different processes will not collide.
+//
+// Unmatched NESTABLE_ASYNC_END event will be parsed as an instant event,
+// and unmatched NESTABLE_ASYNC_BEGIN event will be parsed as an event that
+// ends at the last NESTABLE_ASYNC_END event of that |id|.
+
+// Records a single NESTABLE_ASYNC_BEGIN event called "name" immediately, with 2
+// associated arguments. If the category is not enabled, then this does nothing.
+#define TRACE_EVENT_NESTABLE_ASYNC_BEGIN2(category_group, name, id, arg1_name, \
+        arg1_val, arg2_name, arg2_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_NESTABLE_ASYNC_BEGIN, \
+        category_group, name, id, TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val, \
+        arg2_name, arg2_val)
+// Records a single NESTABLE_ASYNC_END event called "name" immediately, with 2
+// associated arguments. If the category is not enabled, then this does nothing.
+#define TRACE_EVENT_NESTABLE_ASYNC_END2(category_group, name, id, arg1_name, \
+        arg1_val, arg2_name, arg2_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_NESTABLE_ASYNC_END, \
+        category_group, name, id, TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val, \
+        arg2_name, arg2_val)
+// Records a single NESTABLE_ASYNC_INSTANT event called "name" immediately,
+// with 2 associated arguments. If the category is not enabled, then this
+// does nothing.
+#define TRACE_EVENT_NESTABLE_ASYNC_INSTANT2(category_group, name, id, \
+        arg1_name, arg1_val, arg2_name, arg2_val) \
+    INTERNAL_TRACE_EVENT_ADD_WITH_ID(TRACE_EVENT_PHASE_NESTABLE_ASYNC_INSTANT, \
+        category_group, name, id, TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val, \
+        arg2_name, arg2_val)
+
 // Records a single FLOW_BEGIN event called "name" immediately, with 0, 1 or 2
 // associated arguments. If the category is not enabled, then this
 // does nothing.
@@ -963,6 +1004,9 @@ TRACE_EVENT_API_CLASS_EXPORT extern \
 #define TRACE_EVENT_PHASE_ASYNC_STEP_INTO  ('T')
 #define TRACE_EVENT_PHASE_ASYNC_STEP_PAST  ('p')
 #define TRACE_EVENT_PHASE_ASYNC_END   ('F')
+#define TRACE_EVENT_PHASE_NESTABLE_ASYNC_BEGIN ('b')
+#define TRACE_EVENT_PHASE_NESTABLE_ASYNC_END ('e')
+#define TRACE_EVENT_PHASE_NESTABLE_ASYNC_INSTANT ('n')
 #define TRACE_EVENT_PHASE_FLOW_BEGIN ('s')
 #define TRACE_EVENT_PHASE_FLOW_STEP  ('t')
 #define TRACE_EVENT_PHASE_FLOW_END   ('f')