gltrace: Make sure device is debuggable.

Change-Id: Icc22ff823a2f56733b232b927dd1fa494e9e1e81
diff --git a/opengl/libs/EGL/egl.cpp b/opengl/libs/EGL/egl.cpp
index 9e303cf..d46f83b 100644
--- a/opengl/libs/EGL/egl.cpp
+++ b/opengl/libs/EGL/egl.cpp
@@ -124,6 +124,12 @@
 void initEglDebugLevel() {
     int propertyLevel = 0;
     char value[PROPERTY_VALUE_MAX];
+
+    // check system property only on userdebug or eng builds
+    property_get("ro.debuggable", value, "0");
+    if (value[0] == '0')
+        return;
+
     property_get("debug.egl.debug_proc", value, "");
     if (strlen(value) > 0) {
         long pid = getpid();