Clarify the copy-existing-baselines-internal command.

Clarify the copy-existing-baselines-internal command.

Background: The "webkit-patch copy-existing-baselines-internal" command is one of the parts of the layout test rebaseline process which I found a little hard to understand at first. I edited the test earlier, but I think that the code and test could still be made clearer.
Review-Url: https://codereview.chromium.org/2721663003
Cr-Commit-Position: refs/heads/master@{#453760}
Committed: https://chromium.googlesource.com/chromium/src/+/1c0630c164b5be1f0986fe334e1412e8a9d994d2

[qyearsley, 2017-02-27 23:57:08]

Description was changed from

==========
Further clarify the copy-existing-baselines-internal command.
==========

to

==========
Clarify the copy-existing-baselines-internal command.

Background: The "webkit-patch copy-existing-baselines-internal" command is one
of the parts of the layout test rebaseline process which I found a little hard
to understand at first. I edited the test earlier, but I think that the code and
test could still be made clearer.
==========

[qyearsley, 2017-02-27 23:57:08]

qyearsley@chromium.org changed reviewers:
+ jeffcarp@chromium.org

[qyearsley, 2017-02-27 23:58:09]

Jeff, could you check whether this makes any sense, and point out areas that
could be clarified?

This is a non-urgent CL which changes a test but shouldn't affect any actual
behavior.

[jeffcarp, 2017-02-28 21:47:04]

On 2017/02/27 at 23:58:09, qyearsley wrote:
> Jeff, could you check whether this makes any sense, and point out areas that
could be clarified?
> 
> This is a non-urgent CL which changes a test but shouldn't affect any actual
behavior.

I don't have a ton of context on the rebaseline code bug these changes make
sense to me. I don't have anything productive to add. lgtm.

[qyearsley, 2017-02-28 21:49:47]

The CQ bit was checked by qyearsley@chromium.org

[commit-bot: I haz the power, 2017-02-28 21:50:18]

CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[qyearsley, 2017-02-28 21:58:17]

On 2017/02/28 at 21:47:04, jeffcarp wrote:
> On 2017/02/27 at 23:58:09, qyearsley wrote:
> > Jeff, could you check whether this makes any sense, and point out areas that
could be clarified?
> > 
> > This is a non-urgent CL which changes a test but shouldn't affect any actual
behavior.
> 
> I don't have a ton of context on the rebaseline code bug these changes make
sense to me. I don't have anything productive to add. lgtm.

Just for some background about this:

There's a graph of baseline fall-back directories which forms a tree:
https://drive.google.com/open?id=0B9LljzRrCSwXZzNOTlRzQ0RRM0U

Downloading new baselines for a platform may end up overwriting a baseline which
should still be used for another platform. For example, if the results for
mac10.10 and mac10.11 are the same, the baseline might be stored in mac/; if the
baseline for mac10.11 changes but the baseline for mac10.10 doesn't, then the
original baseline in mac/ needs to be backed up to the mac10.10/ directory
first, and that's what "copy-existing-baselines-internal" does.

The reason why I made this CL is that I'm trying to fix something with
`webkit-patch rebaseline-cl`, so I'm trying to understand the related code again
:-P

[commit-bot: I haz the power, 2017-03-01 00:08:02]

CQ is committing da patch.

Bot data: {"patchset_id": 40001, "attempt_start_ts": 1488318587572730,
"parent_rev": "e52268f3f374cb934c4408906b6a09326d284aab", "commit_rev":
"1c0630c164b5be1f0986fe334e1412e8a9d994d2"}

[commit-bot: I haz the power, 2017-03-01 00:09:36]

Description was changed from

==========
Clarify the copy-existing-baselines-internal command.

Background: The "webkit-patch copy-existing-baselines-internal" command is one
of the parts of the layout test rebaseline process which I found a little hard
to understand at first. I edited the test earlier, but I think that the code and
test could still be made clearer.
==========

to

==========
Clarify the copy-existing-baselines-internal command.

Background: The "webkit-patch copy-existing-baselines-internal" command is one
of the parts of the layout test rebaseline process which I found a little hard
to understand at first. I edited the test earlier, but I think that the code and
test could still be made clearer.
Review-Url: https://codereview.chromium.org/2721663003
Cr-Commit-Position: refs/heads/master@{#453760}
Committed:
https://chromium.googlesource.com/chromium/src/+/1c0630c164b5be1f0986fe334e14...
==========

[commit-bot: I haz the power, 2017-03-01 00:09:37]

Committed patchset #3 (id:40001) as
https://chromium.googlesource.com/chromium/src/+/1c0630c164b5be1f0986fe334e14...