Merge changes Ic9b9cef4,I5e807b64

* changes:
  atrace: don't write the clock sync marker if --only_userspace
  atrace: don't hard-fail if one of the categories doesn't exist
diff --git a/cmds/atrace/atrace.cpp b/cmds/atrace/atrace.cpp
index 7aee795..9bd733d 100644
--- a/cmds/atrace/atrace.cpp
+++ b/cmds/atrace/atrace.cpp
@@ -1224,10 +1224,7 @@
 
         if (ret < 0) {
             for (int i = optind; i < argc; i++) {
-                if (!setCategoryEnable(argv[i])) {
-                    fprintf(stderr, "error enabling tracing category \"%s\"\n", argv[i]);
-                    exit(1);
-                }
+                setCategoryEnable(argv[i]);
             }
             break;
         }
@@ -1343,10 +1340,10 @@
         // contain entries from only one CPU can cause "begin" entries without a
         // matching "end" entry to show up if a task gets migrated from one CPU to
         // another.
-        if (!onlyUserspace)
+        if (!onlyUserspace) {
             ok = clearTrace();
-
-        writeClockSyncMarker();
+            writeClockSyncMarker();
+        }
         if (ok && !async && !traceStream) {
             // Sleep to allow the trace to be captured.
             struct timespec timeLeft;