Change sampler code events phase from instant to meta.

base/trace_event/trace_event.h

Index: base/trace_event/trace_event.h
diff --git a/base/trace_event/trace_event.h b/base/trace_event/trace_event.h
index 07018b93e0799c1e9134d694ae170961f5303919..c29d127b07624ee70cd038bd043e8a0915593e6b 100644
--- a/base/trace_event/trace_event.h
+++ b/base/trace_event/trace_event.h
@@ -555,6 +555,20 @@
       TRACE_EVENT_PHASE_SAMPLE, category_group, name, 0, thread_id, timestamp, \
       TRACE_EVENT_FLAG_NONE, arg1_name, arg1_val, arg2_name, arg2_val)
 
+// TRACE_EVENT_METADATA* events are injected by the sampling profiler.
+#define TRACE_EVENT_METADATA0(category_group, name, scope)                   \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_METADATA, category_group, name, \
+                           TRACE_EVENT_FLAG_NONE | scope)
+#define TRACE_EVENT_METADATA1(category_group, name, scope, arg1_name,        \
+                              arg1_val)                                      \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_METADATA, category_group, name, \
+                           TRACE_EVENT_FLAG_NONE | scope, arg1_name, arg1_val)
+#define TRACE_EVENT_METADATA2(category_group, name, scope, arg1_name,          \
+                              arg1_val, arg2_name, arg2_val)                   \
+  INTERNAL_TRACE_EVENT_ADD(TRACE_EVENT_PHASE_METADATA, category_group, name,   \
+                           TRACE_EVENT_FLAG_NONE | scope, arg1_name, arg1_val, \
+                           arg2_name, arg2_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.