[tracing] The CPU profiler should only be enabled for specific modes of tracing

src/profiler/tracing-cpu-profiler.cc

Index: src/profiler/tracing-cpu-profiler.cc
diff --git a/src/profiler/tracing-cpu-profiler.cc b/src/profiler/tracing-cpu-profiler.cc
index 8b3122590500925c312d2a4377d4ede4617d8cb8..4d0559b1e794f844bf57c8f7bc2e1ac03d969c8a 100644
--- a/src/profiler/tracing-cpu-profiler.cc
+++ b/src/profiler/tracing-cpu-profiler.cc
@@ -8,8 +8,11 @@
 #include "src/tracing/trace-event.h"
 #include "src/v8.h"
 
-#define PROFILER_TRACE_CATEGORY_ENABLED(cat) \
-  (*TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED(TRACE_DISABLED_BY_DEFAULT(cat)))
+#define PROFILER_TRACE_CATEGORY_ENABLED(cat)            \
+  (*TRACE_EVENT_API_GET_CATEGORY_GROUP_ENABLED(         \
+      TRACE_DISABLED_BY_DEFAULT(cat)) &                \
+      (kEnabledForRecording_CategoryGroupEnabledFlags | \

[Primiano Tucci (use gerrit), 2017/02/06 23:10:16]

Don't we have the _enabled_for_recording macro  in trace event common? (on a
phone, can't check myself sorry) 

[ssid, 2017/02/07 00:11:54]

ENABLED_FOR_RECORDING is defined in base/trace_event/trace_category.h. Not
included by trace_event_common.

V8 seems to define flags in libplatform
https://chromium.googlesource.com/v8/v8.git/+/667ea83e08afd70b9f9fa15ab304ac7...
and the flags I am using here are defined in v8/src/tracing/trace-event.h.
I am not sure if i can include trace_event_common.h in here.

If you prefer to have the flags moved to trace_event_common.h then i can do it
as different cl and fix V8. Right now I think we need this to fix the crash in
heap profiling.

[Primiano Tucci (use gerrit), 2017/02/07 10:50:14]

So I looked at the code, the situation is the following:
TRACE_EVENT_CATEGORY_GROUP_ENABLED in trace_event_common.h (which is acessible
by v8) is defined as:
...  if (INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE()) ...

which is precisely what we want here.

in turn INTERNAL_TRACE_EVENT_CATEGORY_GROUP_ENABLED_FOR_RECORDING_MODE is
already 
defined in v8/src/tracing/trace-event.h as:
 *INTERNAL_TRACE_EVENT_UID(category_group_enabled) &                    \
      (kEnabledForRecording_CategoryGroupEnabledFlags |                  \
       kEnabledForEventCallback_CategoryGroupEnabledFlags)

so here you are just reinventing existing code.
Unless I am missing something, the right fix here is to:
#define PROFILER_TRACE_CATEGORY_ENABLED(cat, enabled) 
TRACE_EVENT_CATEGORY_GROUP_ENABLED(TRACE_DISABLED_BY_DEFAULT(cat), enabled)

and fix the code below

[alph, 2017/02/07 22:04:31]

+1 for using TRACE_EVENT_CATEGORY_GROUP_ENABLED

[ssid, 2017/02/08 02:24:12]

Ah I didn't realize what you meant. Thanks fixed.

+       kEnabledForEventCallback_CategoryGroupEnabledFlags))
 
 namespace v8 {