Added simplest device mount implementation (includes NullDevice and RandomDevice)

libraries/nacl-mounts/test.nacl/SimpleTest.cc

Index: libraries/nacl-mounts/test.nacl/SimpleTest.cc
===================================================================
--- libraries/nacl-mounts/test.nacl/SimpleTest.cc	(revision 580)
+++ libraries/nacl-mounts/test.nacl/SimpleTest.cc	(working copy)
@@ -14,6 +14,10 @@
   struct stat buf;
   EXPECT_EQ(0, stat("/", &buf));
   EXPECT_EQ(1, S_ISDIR(buf.st_mode));
+  EXPECT_EQ(0, stat("/dev", &buf));
+  EXPECT_EQ(1, S_ISDIR(buf.st_mode));
+  EXPECT_EQ(0, stat("/dev/fd", &buf));
+  EXPECT_EQ(1, S_ISDIR(buf.st_mode));
 
   EXPECT_EQ(-1, stat("/dummy", &buf));
 }