NaCl: Add sanity check for number of open FDs at startup

sandbox/linux/services/credentials_unittest.cc

Index: sandbox/linux/services/credentials_unittest.cc
diff --git a/sandbox/linux/services/credentials_unittest.cc b/sandbox/linux/services/credentials_unittest.cc
index a54ed04ab783379a8da0a899fbae28be4dadad97..90ce11a81734c7dbdcf21fd8376909304e184750 100644
--- a/sandbox/linux/services/credentials_unittest.cc
+++ b/sandbox/linux/services/credentials_unittest.cc
@@ -57,6 +57,17 @@ TEST(Credentials, CreateAndDestroy) {
   scoped_ptr<Credentials> cred2(new Credentials);
 }
 
+TEST(Credentials, CountOpenFds) {
+  base::ScopedFD proc_fd(open("/proc", O_RDONLY | O_DIRECTORY));

[jln (very slow on Chromium), 2014/05/19 21:47:24]

Could you add "ASSERT_TRUE(proc_fd.is_valid());" ?

[Mark Seaborn, 2014/05/19 22:06:11]

Done.

+  Credentials creds;
+  int fd_count = creds.CountOpenFds(proc_fd.get());
+  int fd = open("/dev/null", O_RDONLY);
+  ASSERT_LE(0, fd);
+  EXPECT_EQ(fd_count + 1, creds.CountOpenFds(proc_fd.get()));
+  ASSERT_EQ(0, close(fd));

[jln (very slow on Chromium), 2014/05/19 21:47:24]

IGNORE_EINTR()

[Mark Seaborn, 2014/05/19 22:06:11]

Done.

+  EXPECT_EQ(fd_count, creds.CountOpenFds(proc_fd.get()));
+}
+
 TEST(Credentials, HasOpenDirectory) {
   Credentials creds;
   // No open directory should exist at startup.