Binds two IDs together.

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 faaccac8eaf34b40ff91b81e633df44246266a6a..eca429ac128707ad66dfde1c84c6f8d1820f4c88 100644
--- a/base/trace_event/trace_event.h
+++ b/base/trace_event/trace_event.h
@@ -349,6 +349,37 @@ TRACE_EVENT_API_CLASS_EXPORT extern \
     }                                                                         \
   } while (0)
 
+// The trace ID and bind ID will never be mangled by this macro.
+#define INTERNAL_TRACE_EVENT_ADD_BIND_IDS(category_group, name, id, bind_id,  \
+                                          ...)                                \
+    do {                                                                      \
+      INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group);                 \
+      if (INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE()) { \
+        unsigned int dummy_flags = TRACE_EVENT_FLAG_NONE;                     \
+        trace_event_internal::TraceID trace_event_trace_id(id, &dummy_flags); \

[Primiano Tucci (use gerrit), 2016/07/20 16:39:04]

I think you don't need dummy_flags here and just use TraceID::DontMangle(id)

[chiniforooshan, 2016/07/20 18:41:36]

Done.

+        trace_event_internal::TraceID trace_event_bind_id(                    \

[Primiano Tucci (use gerrit), 2016/07/20 16:39:04]

maybe calling these vars "source_id" and "target_id" instad of "trace_id" and
"bind_id" makes it easier to reason about?

[chiniforooshan, 2016/07/20 18:41:36]

Done.

+            bind_id, &dummy_flags);                                           \
+        if (trace_event_bind_id.scope() ==                                    \
+            trace_event_internal::kGlobalScope) {                             \
+          trace_event_internal::AddTraceEvent(                                \
+              TRACE_EVENT_PHASE_BIND_IDS,                                     \
+              INTERNAL_TRACE_EVENT_UID(category_group_enabled),               \
+              name, trace_event_trace_id.scope(),                             \
+              trace_event_trace_id.raw_id(),                                  \
+              TRACE_EVENT_FLAG_HAS_ID, trace_event_bind_id.raw_id(),          \
+              ##__VA_ARGS__);                                                 \
+        } else {                                                              \
+          trace_event_internal::AddTraceEvent(                                \
+              TRACE_EVENT_PHASE_BIND_IDS,                                     \
+              INTERNAL_TRACE_EVENT_UID(category_group_enabled),               \
+              name, trace_event_trace_id.scope(),                             \
+              trace_event_trace_id.raw_id(),                                  \
+              TRACE_EVENT_FLAG_HAS_ID, trace_event_bind_id.raw_id(),          \
+              "bind_scope", trace_event_bind_id.scope(), ##__VA_ARGS__);      \

[Primiano Tucci (use gerrit), 2016/07/20 16:39:04]

same here, I'd call this arg "target_scope" or "target_bind_scope" or
"bind_target_scope"

[chiniforooshan, 2016/07/20 18:41:36]

I changed the local variable names to {source, target}_id. But, I think it's
better to keep field name "bind_scope" in the args of the actual JSON event,
because we are stuck with the "bind_id" field name at least until tracing V2.

+        }                                                                     \
+      }                                                                       \
+    } while (0)
+
 // Implementation detail: internal macro to create static category and add
 // metadata event if the category is enabled.
 #define INTERNAL_TRACE_EVENT_METADATA_ADD(category_group, name, ...)        \