AU: shift to use new TMPDIR-enabled temp file

The main change here is that delta generator will now create all
temporary files in TMPDIR, if set. Other than that, we're converting all
other temporary file/directory creation to use the new functions.

- All temps of the form "/tmp/foo" are converted to "foo": this
  preserves the behavior in the default case (where TMPDIR is not set),
  yet will do the right thing if run with a different TMPDIR.

- A few other cases (for example, temp file created relative to the
  current working directory) will now be created in TMPDIR or /tmp.
  These are all in unit tests and the transition makes sense anyway.

Note that two temp file/directory creation calls in actual UE code were
using "/tmp/..." and were not changed. This will ensure that they are
resilient to TMPDIR changes and will always be allocated in the same
(hard-coded) location.

BUG=chromium:253622
TEST=Unit tests.

Change-Id: Ia1208963a0e2fcd43b8d6f92bb3d1b7459e930a2
Reviewed-on: https://chromium-review.googlesource.com/182247
Tested-by: Gilad Arnold <garnold@chromium.org>
Reviewed-by: Don Garrett <dgarrett@chromium.org>
Commit-Queue: Gilad Arnold <garnold@chromium.org>
diff --git a/file_writer_unittest.cc b/file_writer_unittest.cc
index 35bfb86..52a50a9 100644
--- a/file_writer_unittest.cc
+++ b/file_writer_unittest.cc
@@ -22,7 +22,7 @@
 TEST(FileWriterTest, SimpleTest) {
   // Create a uniquely named file for testing.
   string path;
-  ASSERT_TRUE(utils::MakeTempFile("/tmp/FileWriterTest-XXXXXX", &path, NULL));
+  ASSERT_TRUE(utils::MakeTempFile("FileWriterTest-XXXXXX", &path, NULL));
   ScopedPathUnlinker path_unlinker(path);
 
   DirectFileWriter file_writer;
@@ -47,7 +47,7 @@
 TEST(FileWriterTest, WriteErrorTest) {
   // Create a uniquely named file for testing.
   string path;
-  ASSERT_TRUE(utils::MakeTempFile("/tmp/FileWriterTest-XXXXXX", &path, NULL));
+  ASSERT_TRUE(utils::MakeTempFile("FileWriterTest-XXXXXX", &path, NULL));
   ScopedPathUnlinker path_unlinker(path);
 
   DirectFileWriter file_writer;