Bug 18800: Remove localhost DNS lookup in nsProfileLock.cpp

Instead of using the local computer's IP address within
symlink-based profile lock signatures, always use 127.0.0.1.

toolkit/profile/nsProfileLock.cpp

@@ -289,18 +289,17 @@ nsresult nsProfileLock::LockWithSymlink(nsIFile* aLockFile,
   if (!mReplacedLockTime)
     aLockFile->GetLastModifiedTimeOfLink(&mReplacedLockTime);
 
+  // For Tor Browser, avoid a DNS lookup here so the Tor network is not
+  // bypassed. Instead, always use 127.0.0.1 for the IP address portion
+  // of the lock signature, which may cause the browser to refuse to
+  // start in the rare event that all of the following conditions are met:
+  //   1. The browser profile is on a network file system.
+  //   2. The file system does not support fcntl() locking.
+  //   3. Tor Browser is run from two different computers at the same time.
+
   struct in_addr inaddr;
   inaddr.s_addr = htonl(INADDR_LOOPBACK);
 
-  char hostname[256];
-  PRStatus status = PR_GetSystemInfo(PR_SI_HOSTNAME, hostname, sizeof hostname);
-  if (status == PR_SUCCESS) {
-    char netdbbuf[PR_NETDB_BUF_SIZE];
-    PRHostEnt hostent;
-    status = PR_GetHostByName(hostname, netdbbuf, sizeof netdbbuf, &hostent);
-    if (status == PR_SUCCESS) memcpy(&inaddr, hostent.h_addr, sizeof inaddr);
-  }
-
   mozilla::SmprintfPointer signature =
       mozilla::Smprintf("%s:%s%lu", inet_ntoa(inaddr),
                         aHaveFcntlLock ? "+" : "", (unsigned long)getpid());