Add granular file tracing.

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 e0249f5539a181175127ba4df1cc7fc489328f44..57a6850a957e2deba5e50e57ea499a4ab8c8bbce 100644
--- a/base/trace_event/trace_event.h
+++ b/base/trace_event/trace_event.h
@@ -234,6 +234,19 @@
   INTERNAL_TRACE_EVENT_ADD_SCOPED( \
       category_group, name, arg1_name, arg1_val, arg2_name, arg2_val)
 
+// Records a pair of begin and end events called "name" for the current scope
+// with 1 or 2 associated arguments. These events are associated with id. If the
+// category is not enabled, this does nothing.
+// - category and name strings must have application lifetime (statics or
+//   literals). They may not include " chars.
+#define TRACE_EVENT_ID1(category_group, name, id, arg1_name, arg1_val) \
+  INTERNAL_TRACE_EVENT_ADD_SCOPED_WITH_ID( \
+      category_group, name, id, arg1_name, arg1_val)

[Sami, 2015/04/29 15:01:51]

It's not clear what |id| refers to here. Does it need to match the ASYNC id?

Could you upload a sample trace with this data in it just to get an idea of how
this looks? I'm wondering if the NESTABLE_ASYNC event would be more appropriate.

[Dan Beam, 2015/04/30 04:40:13]

yes
it probably is.  shared a TRACE_EVENT_ID* version with everybody (before I try
TRACE_EVENT_NESTABLE*).

+#define TRACE_EVENT_ID2( \
+    category_group, name, id, arg1_name, arg1_val, arg2_name, arg2_val) \
+  INTERNAL_TRACE_EVENT_ADD_SCOPED_WITH_ID( \
+      category_group, name, id, arg1_name, arg1_val, arg2_name, arg2_val)
+
 // Records events like TRACE_EVENT2 but uses |memory_tag| for memory tracing.
 // Use this where |name| is too generic to accurately aggregate allocations.
 #define TRACE_EVENT_WITH_MEMORY_TAG2( \
@@ -1009,6 +1022,26 @@ TRACE_EVENT_API_CLASS_EXPORT extern \
           INTERNAL_TRACE_EVENT_UID(category_group_enabled), name, h); \
     }
 
+// Implementation detail: internal macro to create static category and add begin
+// event if the category is enabled. Also adds the end event when the scope
+// ends.
+#define INTERNAL_TRACE_EVENT_ADD_SCOPED_WITH_ID(category_group, name, id, ...) \
+    INTERNAL_TRACE_EVENT_GET_CATEGORY_INFO(category_group); \
+    trace_event_internal::ScopedTracer INTERNAL_TRACE_EVENT_UID(tracer); \
+    if (INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE()) { \
+      unsigned char trace_event_flags = TRACE_EVENT_FLAG_HAS_ID; \
+      trace_event_internal::TraceID trace_event_trace_id( \
+          id, &trace_event_flags); \
+      base::trace_event::TraceEventHandle h = \
+          trace_event_internal::AddTraceEvent( \
+              TRACE_EVENT_PHASE_COMPLETE, \
+              INTERNAL_TRACE_EVENT_UID(category_group_enabled), name, \
+              trace_event_trace_id.data(), trace_event_flags, \
+              ##__VA_ARGS__); \
+      INTERNAL_TRACE_EVENT_UID(tracer).Initialize( \
+          INTERNAL_TRACE_EVENT_UID(category_group_enabled), name, h); \
+    }
+
 // Implementation detail: internal macro to create static category and add
 // event if the category is enabled.
 #define INTERNAL_TRACE_EVENT_ADD_WITH_ID(phase, category_group, name, id, \