tracing: Actually fix track_uuid association for typed events

Follow-up to crrev.com/c/2644798. The symbol also needs to be exported
and defined in a .cc.

Bug: 1168791
Change-Id: I0c7308bfe24846381d3dcad00e8d76f337909634
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2645005Reviewed-by: Sami Kyöstilä <skyostil@chromium.org>
Commit-Queue: Sami Kyöstilä <skyostil@chromium.org>
Cr-Commit-Position: refs/heads/master@{#846241}

base/trace_event/typed_macros_internal.cc

@@ -51,6 +51,10 @@ GetPhaseAndIdForTraceLog(bool explicit_track, uint64_t track_uuid, char phase) {
 
 }  // namespace
 
+namespace trace_event_internal {
+const perfetto::Track kDefaultTrack{};
+}  // namespace trace_event_internal
+
 namespace base {
 namespace trace_event {
 

base/trace_event/typed_macros_internal.h

@@ -59,7 +59,7 @@
 
 namespace trace_event_internal {
 
-static const perfetto::Track kDefaultTrack{};
+extern BASE_EXPORT const perfetto::Track kDefaultTrack;
 
 // Copy of function with the same name from Perfetto client library.
 template <typename T>