I mounted my chrome checkout in my chroot using cros_sdk --chrome_root=...

When I emerge chromeos-chrome I get the following error to do with not having permission to the /mnt/host/depot_tools/metrics.cfg file.

(cr) ((474ae60...)) raymes@raymes ~/trunk/src/scripts $ emerge-caroline-arcnext chromeos-chrome
Calculating dependencies... done!

>>> Emerging (1 of 1) chromeos-base/chromeos-chrome-9999::chromiumos for /build/caroline-arcnext/
 * Running stacked hooks for pre_pkg_setup
 *    sysroot_build_bin_dir ...                                                                                                  [ ok ]
 * Running stacked hooks for post_pkg_setup
 *    python_eclass_hack ...                                                                                                     [ ok ]
 * Running stacked hooks for pre_src_unpack
 *    python_multilib_setup ...                                                                                                  [ ok ]
>>> Unpacking source...
 * CHROME_ORIGIN VALUE is LOCAL_SOURCE
 * Using GN from /home/raymes/chrome_root/src/buildtools/linux64/gn
>>> Source unpacked in /build/caroline-arcnext/tmp/portage/chromeos-base/chromeos-chrome-9999/work
 * Running stacked hooks for post_src_unpack
 *    asan_init ...                                                                                                              [ ok ]
 * Running stacked hooks for pre_src_prepare
 *    enable_cxx_exceptions ...                                                                                                  [ ok ]
>>> Preparing source in /build/caroline-arcnext/tmp/portage/chromeos-base/chromeos-chrome-9999/work/chromeos-chrome-9999 ...
 * /home/raymes/chrome_root should be set here properly
>>> Source prepared.
>>> Configuring source in /build/caroline-arcnext/tmp/portage/chromeos-base/chromeos-chrome-9999/work/chromeos-chrome-9999 ...
 * Using gold from the following location: /usr/x86_64-pc-linux-gnu/x86_64-cros-linux-gnu/binutils-bin/2.27.0-gold
 * Building with the compiler settings:
 *   CFLAGS = -pipe -pipe -march=corei7 -fno-split-dwarf-inlining -fdebug-info-for-profiling -Wno-unknown-warning-option
 *   CXXFLAGS = -pipe -pipe -pipe -march=corei7 -fno-split-dwarf-inlining -fdebug-info-for-profiling -D__google_stl_debug_vector=1 -Wno-unknown-warning-option -stdlib=libc++
 *   CPPFLAGS = 
 *   LDFLAGS = -Wl,-O1 -Wl,-O2 -Wl,--as-needed -stdlib=libc++
/mnt/host/depot_tools/gclient runhooks --force

*****************************************************
*  METRICS COLLECTION WILL START IN 10 EXECUTIONS   *
*                                                   *
* For more information, and for how to disable this *
* message, please see metrics.README.md in your     *
* depot_tools checkout.                             *
*****************************************************

 * ACCESS DENIED:  fopen_wr:     /mnt/host/depot_tools/metrics.cfg
Traceback (most recent call last):
  File "/mnt/host/depot_tools/gclient.py", line 3029, in <module>
    sys.exit(main(sys.argv[1:]))
  File "/mnt/host/depot_tools/gclient.py", line 3015, in main
    return dispatcher.execute(OptionParser(), argv)
  File "/mnt/host/depot_tools/subcommand.py", line 252, in execute
    return command(parser, args[1:])
  File "/mnt/host/depot_tools/metrics.py", line 199, in _inner
    self._collect_metrics(func, command_name, *args, **kwargs)
  File "/mnt/host/depot_tools/metrics.py", line 140, in _collect_metrics
    self.config.decrease_countdown()
  File "/mnt/host/depot_tools/metrics.py", line 103, in decrease_countdown
    self._write_config()
  File "/mnt/host/depot_tools/metrics.py", line 75, in _write_config
    gclient_utils.FileWrite(CONFIG_FILE, json.dumps(self._config))
  File "/mnt/host/depot_tools/gclient_utils.py", line 150, in FileWrite
    with codecs.open(filename, mode=mode, encoding='utf-8') as f:
  File "/usr/lib64/python2.7/codecs.py", line 884, in open
    file = __builtin__.open(filename, mode, buffering)
IOError: [Errno 13] Permission denied: '/mnt/host/depot_tools/metrics.cfg'
 * ERROR: chromeos-base/chromeos-chrome-9999::chromiumos failed (configure phase):
 *   (no error message)