Add a way to turn off unique_fd's operator int.

unique_fd's implicit conversion to int has led to tons of problems (see
all of the overloads for close, fdopen, fdopendir, etc.). Add a switch
that can turn it off, and reduce the ridiculous amount of work to fix up
callers by introducing a borrowed_fd type that can be constructed from
either int or unique_fd.

Test: treehugger
Change-Id: If77cf5cbcaddacdaec5919a15b3520fb68f51a62
diff --git a/cmsg.cpp b/cmsg.cpp
index 42866f8..1fa873c 100644
--- a/cmsg.cpp
+++ b/cmsg.cpp
@@ -29,7 +29,7 @@
 namespace android {
 namespace base {
 
-ssize_t SendFileDescriptorVector(int sockfd, const void* data, size_t len,
+ssize_t SendFileDescriptorVector(borrowed_fd sockfd, const void* data, size_t len,
                                  const std::vector<int>& fds) {
   size_t cmsg_space = CMSG_SPACE(sizeof(int) * fds.size());
   size_t cmsg_len = CMSG_LEN(sizeof(int) * fds.size());
@@ -67,10 +67,10 @@
   int flags = 0;
 #endif
 
-  return TEMP_FAILURE_RETRY(sendmsg(sockfd, &msg, flags));
+  return TEMP_FAILURE_RETRY(sendmsg(sockfd.get(), &msg, flags));
 }
 
-ssize_t ReceiveFileDescriptorVector(int sockfd, void* data, size_t len, size_t max_fds,
+ssize_t ReceiveFileDescriptorVector(borrowed_fd sockfd, void* data, size_t len, size_t max_fds,
                                     std::vector<unique_fd>* fds) {
   fds->clear();
 
@@ -98,7 +98,7 @@
   flags |= MSG_CMSG_CLOEXEC | MSG_NOSIGNAL;
 #endif
 
-  ssize_t rc = TEMP_FAILURE_RETRY(recvmsg(sockfd, &msg, flags));
+  ssize_t rc = TEMP_FAILURE_RETRY(recvmsg(sockfd.get(), &msg, flags));
 
   if (rc == -1) {
     return -1;