tracing: Add an option for disabling markers

In our application, we have trace markers spread through user-space.
We have markers in GL, X, etc. These are super handy for Chrome's
about:tracing feature (Chrome + system + kernel trace view), but
can be very distracting when you're trying to debug a kernel issue.

I normally, use "grep -v tracing_mark_write" but it would be nice
if I could just temporarily disable markers all together.

Link: http://lkml.kernel.org/r/1347066739-26285-1-git-send-email-msb@chromium.org

CC: Frederic Weisbecker <fweisbec@gmail.com>
Signed-off-by: Mandeep Singh Baines <msb@chromium.org>
Signed-off-by: Steven Rostedt <rostedt@goodmis.org>
diff --git a/kernel/trace/trace.h b/kernel/trace/trace.h
index 593debe..63a2da0 100644
--- a/kernel/trace/trace.h
+++ b/kernel/trace/trace.h
@@ -680,6 +680,7 @@
 	TRACE_ITER_OVERWRITE		= 0x200000,
 	TRACE_ITER_STOP_ON_FREE		= 0x400000,
 	TRACE_ITER_IRQ_INFO		= 0x800000,
+	TRACE_ITER_MARKERS		= 0x1000000,
 };
 
 /*