Add an explicit way of making IDs local or global

base/trace_event/trace_event_impl.cc

Index: base/trace_event/trace_event_impl.cc
diff --git a/base/trace_event/trace_event_impl.cc b/base/trace_event/trace_event_impl.cc
index 510cc2ffac6b32add118eb53ed4147b4b70369d9..349e54ebc7a4ebd4d9d4be380a0442c21949d617 100644
--- a/base/trace_event/trace_event_impl.cc
+++ b/base/trace_event/trace_event_impl.cc
@@ -358,10 +358,15 @@ void TraceEvent::AppendAsJSON(
 
   // If id_ is set, print it out as a hex string so we don't loose any
   // bits (it might be a 64-bit pointer).
-  if (flags_ & TRACE_EVENT_FLAG_HAS_ID) {
+  unsigned int id_flags = flags_ & TRACE_EVENT_FLAG_ID_MASK;
+  if (id_flags != TRACE_EVENT_FLAG_NONE) {
     if (scope_ != trace_event_internal::kGlobalScope)
       StringAppendF(out, ",\"scope\":\"%s\"", scope_);
     StringAppendF(out, ",\"id\":\"0x%" PRIx64 "\"", static_cast<uint64_t>(id_));
+    if (id_flags == TRACE_EVENT_FLAG_HAS_LOCAL_ID)
+      *out += ",\"id_is_global\":false";

[caseq, 2016/08/22 19:48:52]

rather than emitting it as a bool flag, can we vary the field name instead? I.e.
only emit "id" if the id is global and call it "localId" otherwise for async
events?

[chiniforooshan, 2016/08/23 19:54:53]

Is there anything wrong with using a boolean here? Without the boolean, wouldn't
the "id" field be ambiguous for importers? It can mean "global ID" if the trace
is new or have a type-related scope if the trace is old (and there is no way of
finding out which one it is).

+    if (id_flags == TRACE_EVENT_FLAG_HAS_GLOBAL_ID)
+      *out += ",\"id_is_global\":true";
   }
 
   if (flags_ & TRACE_EVENT_FLAG_BIND_TO_ENCLOSING)