Add PERFETTO_DFATAL.

Replace all uses of DCHECK(false) with it.

Change-Id: I95f83cc462d3f7310a54cf1117c32fa04fee32e8
diff --git a/src/traced/probes/probes_producer.cc b/src/traced/probes/probes_producer.cc
index d91f066..65c0890 100644
--- a/src/traced/probes/probes_producer.cc
+++ b/src/traced/probes/probes_producer.cc
@@ -335,7 +335,7 @@
       case SysStatsDataSource::kTypeId:
         break;
       default:
-        PERFETTO_DCHECK(false);
+        PERFETTO_DFATAL("Invalid data source.");
     }  // switch (type_id)
   }    // for (session_data_sources_)
 }