libutils: add a system-wide tracing utility

This change adds some utility functionality for doing userland tracing
into the kernel trace log.

Change-Id: Id0a8cee9ea515b1d8765afd1cecf472a88b4b9e8
diff --git a/libs/utils/Android.mk b/libs/utils/Android.mk
index a96c8e6..57c048a 100644
--- a/libs/utils/Android.mk
+++ b/libs/utils/Android.mk
@@ -77,7 +77,8 @@
 # we have the common sources, plus some device-specific stuff
 LOCAL_SRC_FILES:= \
 	$(commonSources) \
-	Looper.cpp
+	Looper.cpp \
+	Trace.cpp
 
 ifeq ($(TARGET_OS),linux)
 LOCAL_LDLIBS += -lrt -ldl