Allow $TMPDIR to set temporary directory on OS X.

chrome/browser/file_select_helper_mac.mm

Index: chrome/browser/file_select_helper_mac.mm
diff --git a/chrome/browser/file_select_helper_mac.mm b/chrome/browser/file_select_helper_mac.mm
index 2fdc57923d89d5f85f3039c61731c152fd150145..db910f8076e40e7ba2f5631ee303ac80f02428e7 100644
--- a/chrome/browser/file_select_helper_mac.mm
+++ b/chrome/browser/file_select_helper_mac.mm
@@ -20,18 +20,24 @@ 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();
+  }
+
+  // TMPDIR/<bundleID>/zip_cache/<GUID>
+
+  NSString* bundleID = [[NSBundle mainBundle] bundleIdentifier];
+  dest.Append(base::mac::NSStringToString(bundleID))
+
+  dest.Append("zip_cache")
 
-  [dest appendFormat:@"%@/zip_cache/%@",
-                     [[NSBundle mainBundle] bundleIdentifier],
-                     [[NSProcessInfo processInfo] globallyUniqueString]];
+  NSString* GUID = [[NSProcessInfo processInfo] globallyUniqueString];
+  dest.Append(base::mac::NSStringToString(GUID))
 
-  return base::mac::NSStringToFilePath(dest);
+  return dest;
 }
 
 // Returns the path of the package and its components relative to the package's