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..2fda2a1e6e9e2970e99d04b0ea0c41bcdc339496 100644
--- a/sandbox/linux/services/credentials_unittest.cc
+++ b/sandbox/linux/services/credentials_unittest.cc
@@ -57,6 +57,20 @@ TEST(Credentials, CreateAndDestroy) {
   scoped_ptr<Credentials> cred2(new Credentials);
 }
 
+TEST(Credentials, CountOpenFds) {
+  int proc_fd = open("/proc", O_RDONLY | O_DIRECTORY);
+  ASSERT_LE(0, proc_fd);
+  base::ScopedFD proc_fd_closer(proc_fd);

[jln (very slow on Chromium), 2014/05/09 23:55:24]

Now that ScopedFD have been rewritten, they're not longer "pure closers".

So simply do base::ScopedFD proc_fd(open(..));
and use proc_fd.get()

[Mark Seaborn, 2014/05/19 21:38:21]

Done.

+
+  Credentials creds;
+  int fd_count = creds.CountOpenFds(proc_fd);
+  int fd = open("/dev/null", O_RDONLY);
+  ASSERT_LE(0, fd);
+  EXPECT_EQ(fd_count + 1, creds.CountOpenFds(proc_fd));
+  ASSERT_EQ(0, close(fd));
+  EXPECT_EQ(fd_count, creds.CountOpenFds(proc_fd));
+}
+
 TEST(Credentials, HasOpenDirectory) {
   Credentials creds;
   // No open directory should exist at startup.