Pass a FD to resise_file and add a testcase.

I will add a real use in another commit.

llvm-svn: 224136
diff --git a/llvm/unittests/Support/Path.cpp b/llvm/unittests/Support/Path.cpp
index 81d9234..88baade 100644
--- a/llvm/unittests/Support/Path.cpp
+++ b/llvm/unittests/Support/Path.cpp
@@ -638,6 +638,16 @@
 }
 #endif
 
+TEST_F(FileSystemTest, Resize) {
+  int FD;
+  SmallString<64> TempPath;
+  ASSERT_NO_ERROR(fs::createTemporaryFile("prefix", "temp", FD, TempPath));
+  ASSERT_NO_ERROR(fs::resize_file(FD, 123));
+  fs::file_status Status;
+  ASSERT_NO_ERROR(fs::status(FD, Status));
+  ASSERT_EQ(Status.getSize(), 123U);
+}
+
 TEST_F(FileSystemTest, FileMapping) {
   // Create a temp file.
   int FileDescriptor;