Fix 'git cl format' on windows metrics files
Fix 'git cl format' on windows metrics files

The issue is with directory separators:
"Check that c:\src\chromium\src or 
c:\src\chromium\src\tools/metrics/histograms/pretty_print.py
exist and have execution permission."

BUG=679514

Change-Id: I88a57783ca3bf8aa5af4d83fb34901c2d2385fe9
Reviewed-on: https://chromium-review.googlesource.com/457800
Reviewed-by: Robbie Iannucci <40f3d43a28ebae3cb819288542e1c84d73d962d5@chromium.org>
Commit-Queue: Pierre-Antoine Manzagol <16fbbc88744c90cca86069e67f23f20ad78787d3@chromium.org>

CoherentLabs/depot_tools,CoherentLabs/depot_tools