Add atrace event for perfetto_hprof init.

Bug: 147577567
Bug: 147667830

Change-Id: If6528e2544a19cd4af6f21630fabe84434c1c1ef
diff --git a/runtime/runtime.cc b/runtime/runtime.cc
index d8795ab..32de85a 100644
--- a/runtime/runtime.cc
+++ b/runtime/runtime.cc
@@ -1050,6 +1050,7 @@
   ScopedObjectAccess soa(Thread::Current());
   if (Dbg::IsJdwpAllowed() || IsProfileableFromShell() || IsJavaDebuggable()) {
     std::string err;
+    ScopedTrace tr("perfetto_hprof init.");
     ScopedThreadSuspension sts(Thread::Current(), ThreadState::kNative);
     if (!EnsurePerfettoPlugin(&err)) {
       LOG(WARNING) << "Failed to load perfetto_hprof: " << err;