[XRay] Use explicit string conversion

Instead of using std::copy(...), use a conversion to string instead from
StringRef to std::string.

llvm-svn: 346304

llvm/lib/XRay/FDRTraceExpander.cpp

@@ -45,8 +45,7 @@ Error TraceExpander::visit(CustomEventRecord &R) {
     CurrentRecord.PId = PID;
     CurrentRecord.TId = TID;
     CurrentRecord.Type = RecordTypes::CUSTOM_EVENT;
-    std::copy(R.data().begin(), R.data().end(),
-              std::back_inserter(CurrentRecord.Data));
+    CurrentRecord.Data = R.data();
     BuildingRecord = true;
   }
   return Error::success();