Make unittests work in component build

src/heap/gc-tracer.h

Index: src/heap/gc-tracer.h
diff --git a/src/heap/gc-tracer.h b/src/heap/gc-tracer.h
index 67d7a18caf43bea51dd511f57315ec71317dd833..6fbde83b0f82f9dae1f7a05aeab0b141b8d09379 100644
--- a/src/heap/gc-tracer.h
+++ b/src/heap/gc-tracer.h
@@ -95,7 +95,7 @@ enum ScavengeSpeedMode { kForAllObjects, kForSurvivedObjects };
 
 // GCTracer collects and prints ONE line after each garbage collector
 // invocation IFF --trace_gc is used.
-class GCTracer {
+class V8_EXPORT_PRIVATE GCTracer {
  public:
   struct IncrementalMarkingInfos {
     IncrementalMarkingInfos() : duration(0), longest_step(0), steps(0) {}