Add tracing initialization to init.rc.

This change adds init.rc steps to allow kernel tracing to support inserting
messages from any userland process.

Change-Id: I01970728d7132a25408fed09a213a015ac05ccaf
diff --git a/rootdir/init.rc b/rootdir/init.rc
index 71ec3fa..dfe2479 100644
--- a/rootdir/init.rc
+++ b/rootdir/init.rc
@@ -370,6 +370,10 @@
 on property:ro.debuggable=1
     start console
 
+# Allow writing to the kernel trace log.  Enabling tracing still requires root.
+on property:ro.debuggable=1
+    chmod 0222 /sys/kernel/debug/tracing/trace_marker
+
 # adbd is controlled via property triggers in init.<platform>.usb.rc
 service adbd /sbin/adbd
     class core