Trace events corresponding to GCTracer scopes.

src/heap/gc-tracer.cc

Index: src/heap/gc-tracer.cc
diff --git a/src/heap/gc-tracer.cc b/src/heap/gc-tracer.cc
index 880f8ef98c6e023caf6b4c65dcd6bac9c3e2a310..3c46f5292dfdd2d37e39e2da0e35c52627c6ffeb 100644
--- a/src/heap/gc-tracer.cc
+++ b/src/heap/gc-tracer.cc
@@ -44,6 +44,18 @@ GCTracer::Scope::~Scope() {
   }
 }
 
+const char* GCTracer::Scope::Name(ScopeId id) {
+#define CASE(scope)  \
+  case Scope::scope: \
+    return "V8.GC_" #scope;
+  switch (id) {
+    TRACER_SCOPES(CASE)
+    case Scope::NUMBER_OF_SCOPES:
+      break;
+  }
+#undef CASE
+  return "(unknown)";
+}
 
 GCTracer::Event::Event(Type type, const char* gc_reason,
                        const char* collector_reason)