Teach update_from_chromium.py to preserve certain files through roll.

Teach update_from_chromium.py to preserve certain files through roll.

This CL adds a step to the process of rolling from Chromium wherein a specified
set of files have their contents preserved through the roll even though they
live in directories rolled in from Chromium.

The first usage of this infrastructure is to support the existence of a
//build/config/mojo.gni file that differs between Mojo and Chromium.

//build/config/mojo.gni will start being used in a followup CL.

R=jamesr@chromium.org

Committed: https://chromium.googlesource.com/external/mojo/+/977e2fec0fa3eaf70bd873fc5f537a2aa59b266d

[blundell, 2015-01-28 10:21:03]

blundell@chromium.org changed reviewers:
+ jamesr@chromium.org

[blundell, 2015-01-30 15:19:30]

ping.

[jamesr, 2015-01-31 01:50:50]

Why can't you teach the roll script to just preserve certain files in-place
rather than having this secondary directory?  i.e.

for x in files_to_preserve:
  copy x from src_path to tmpdir

do roll

for x in files_to_preserve
  copy x from tmpdir to src_path

?

Having a second copy of the file somewhere else seems really confusing and I
can't see why it would be needed.

[blundell, 2015-02-02 20:10:26]

Done.

[jamesr, 2015-02-02 20:28:09]

Actually we have a copy of the previous version in git - why not just use that?
i.e. 'git checkout -- path/to/...'?

[jamesr, 2015-02-02 20:28:45]

https://codereview.chromium.org/864953003/diff/120001/build/config/mojo.gni
File build/config/mojo.gni (right):

https://codereview.chromium.org/864953003/diff/120001/build/config/mojo.gni#n...
build/config/mojo.gni:1: # Copyright 2015 The Chromium Authors. All rights
reserved.
don't do this

[blundell, 2015-02-02 21:08:46]

Patchset #8 (id:140001) has been deleted

[blundell, 2015-02-02 21:15:58]

Changed to restore the pre-roll rev.

https://codereview.chromium.org/864953003/diff/120001/build/config/mojo.gni
File build/config/mojo.gni (right):

https://codereview.chromium.org/864953003/diff/120001/build/config/mojo.gni#n...
build/config/mojo.gni:1: # Copyright 2015 The Chromium Authors. All rights
reserved.
On 2015/02/02 20:28:45, jamesr wrote:
> don't do this

This is a new file that git is treating as a copy.

[jamesr, 2015-02-02 21:26:56]

lgtm

https://codereview.chromium.org/864953003/diff/130004/mojo/tools/roll/update_...
File mojo/tools/roll/update_from_chromium.py (right):

https://codereview.chromium.org/864953003/diff/130004/mojo/tools/roll/update_...
mojo/tools/roll/update_from_chromium.py:139: commit("Restored pre-roll versions
of files that don't get rolled")
commit after the loop (you don't want to commit for every single file) and skip
this commit if the files_to_not_roll is empty

[blundell, 2015-02-03 08:26:35]

Committed patchset #9 (id:170001) manually as
977e2fec0fa3eaf70bd873fc5f537a2aa59b266d (presubmit successful).

[blundell, 2015-02-03 08:29:48]

https://codereview.chromium.org/864953003/diff/130004/mojo/tools/roll/update_...
File mojo/tools/roll/update_from_chromium.py (right):

https://codereview.chromium.org/864953003/diff/130004/mojo/tools/roll/update_...
mojo/tools/roll/update_from_chromium.py:139: commit("Restored pre-roll versions
of files that don't get rolled")
On 2015/02/02 21:26:56, jamesr wrote:
> commit after the loop (you don't want to commit for every single file) and
skip
> this commit if the files_to_not_roll is empty

Done.