OS: macOS 10.12.4

What steps will reproduce the problem?
(1) Run `gn args out/ios-debug` on the repo src. It has a space in the full path.
(2) Run ninja -C out/ios-debug ios_remoting_app

What is the expected result?

It builds

What happens instead?

Saw this error:
[1/1] Regenerating ninja files
FAILED: build.ninja 
/Volumes/Mac Data/chromium/src/buildtools/mac/gn --root=/Volumes/Mac Data/chromium/src -q gen .
/bin/sh: /Volumes/Mac: No such file or directory
ninja: error: rebuilding 'build.ninja': subcommand failed

Here is the beginning of the out/ios-debug/build.ninja file:
rule gn
  command = /Volumes/Mac Data/chromium/src/buildtools/mac/gn --root=/Volumes/Mac Data/chromium/src -q gen .
  description = Regenerating ninja files

Apparently the --root parameter is not being quoted.