Do fcntl(...F_FULLFSYNC...) on mac instead of fsync

From mac's fsync man page:

For applications that require tighter guarantees about the integrity of their
data, Mac OS X provides the F_FULLFSYNC fcntl.  The F_FULLFSYNC fcntl asks the
drive to flush all buffered data to permanent storage.  Applications, such as
databases, that require a strict ordering of writes should use F_FULLFSYNC to
ensure that their data is written in the order they expect.

Also, specifically check for a return value of -1 from fdatasync. mac's fcntl
only guarantees to return -1 on error and something other than -1 on success.
All other platforms agree to return -1 on error for fsync/fdatasync/_commit.

Review URL: https://chromiumcodereview.appspot.com/23549017

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@221413 0039d316-1c4b-4281-b951-d872f2087c98

third_party/leveldatabase/env_chromium.cc

@@ -68,6 +68,8 @@ int fflush_wrapper(FILE *file) {
 int fdatasync(int fildes) {
 #if defined(OS_WIN)
   return _commit(fildes);
+#elif defined(OS_MACOSX)
+  return HANDLE_EINTR(fcntl(fildes, F_FULLFSYNC, 0));
 #else
   return HANDLE_EINTR(fsync(fildes));
 #endif
@@ -510,7 +512,7 @@ Status ChromiumWritableFile::Sync() {
     error = errno;
   // Sync even if fflush gave an error; perhaps the data actually got out,
   // even though something went wrong.
-  if (fdatasync(fileno(file_)) && !error)
+  if (fdatasync(fileno(file_)) == -1 && !error)
     error = errno;
   // Report the first error we found.
   if (error) {