Allow $TMPDIR to set temporary directory on OS X.

chrome/browser/file_select_helper_mac.mm

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "chrome/browser/file_select_helper.h"
 
 #include <Cocoa/Cocoa.h>
 #include <sys/stat.h>
 
 #include "base/files/file.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/mac/foundation_util.h"
 #include "content/public/browser/browser_thread.h"
 #include "third_party/zlib/google/zip.h"
 #include "ui/shell_dialogs/selected_file_info.h"
 
 namespace {
 
 // Given the |path| of a package, returns the destination that the package
 // should be zipped to. Returns an empty path on any errors.

[iannucci, 2017/02/24 20:56:01]

This comment seems... misleading at best? `path` is not consulted in the old
code at all.

 base::FilePath ZipDestination(const base::FilePath& path) {
-  NSMutableString* dest =
-      [NSMutableString stringWithString:NSTemporaryDirectory()];
+  base::FilePath dest;
 
-  // Couldn't get the temporary directory.
-  if (!dest)
+  if (!base::GetTempDir(dest)) {
+    // Couldn't get the temporary directory.
     return base::FilePath();
+  }
 
-  [dest appendFormat:@"%@/zip_cache/%@",
-                     [[NSBundle mainBundle] bundleIdentifier],
-                     [[NSProcessInfo processInfo] globallyUniqueString]];
+  // TMPDIR/<bundleID>/zip_cache/<GUID>
 
-  return base::mac::NSStringToFilePath(dest);
+  NSString* bundleID = [[NSBundle mainBundle] bundleIdentifier];
+  dest.Append(base::mac::NSStringToString(bundleID))
+
+  dest.Append("zip_cache")
+
+  NSString* GUID = [[NSProcessInfo processInfo] globallyUniqueString];
+  dest.Append(base::mac::NSStringToString(GUID))
+
+  return dest;
 }
 
 // Returns the path of the package and its components relative to the package's
 // parent directory.
 std::vector<base::FilePath> RelativePathsForPackage(
     const base::FilePath& package) {
   // Get the base directory.
   base::FilePath base_dir = package.DirName();
 
   // Add the package as the first relative path.
@@ skipping 86 matching lines @@
     // need to be deleted now.
     if (!web_contents_) {
       DeleteTemporaryFiles();
       RunFileChooserEnd();
       return;
     }
   }
 
   NotifyRenderFrameHostAndEnd(files);
 }