Add a GN auto-roller script.

Add a GN auto-roller script.

This CL adds a script in //tools/gn/bin/roll_gn.py that, given no
arguments, will post three CLs and three tryjobs in order to:
  * build a new GN binary at tip-of-tree
  * update the buildtools repo to the newly built binaries
  * and then update DEPS to point to the leatest buildtools

The script must be run on Linux by someone with commit access to both
src/ and buildtools/.

One can also run the steps independently for testing purposes.

It can only be run in a clean chromium checkout; it should error out
in most cases if something bad happens, but the error checking isn't
yet foolproof.

R=brettw@chromium.org, scottmg@chromium.org, thakis@chromium.org

Committed: https://crrev.com/97ec9ac8703dc10eaef5e60984bb3ecdfad344bd
Cr-Commit-Position: refs/heads/master@{#339191}

[brettw, 2015-07-15 01:59:05]

I only skimmed the code. LGTM with the additions below.

https://codereview.chromium.org/1230293003/diff/20001/tools/gn/bin/roll_gn.py
File tools/gn/bin/roll_gn.py (right):

https://codereview.chromium.org/1230293003/diff/20001/tools/gn/bin/roll_gn.py...
tools/gn/bin/roll_gn.py:1: #!/usr/bin/python
Needs copyright.

https://codereview.chromium.org/1230293003/diff/20001/tools/gn/bin/roll_gn.py...
tools/gn/bin/roll_gn.py:15: depot_tools_path = None
Can this have some documentation and an example at the top?

[Dirk Pranke, 2015-07-15 02:40:32]

https://codereview.chromium.org/1230293003/diff/20001/tools/gn/bin/roll_gn.py
File tools/gn/bin/roll_gn.py (right):

https://codereview.chromium.org/1230293003/diff/20001/tools/gn/bin/roll_gn.py...
tools/gn/bin/roll_gn.py:1: #!/usr/bin/python
On 2015/07/15 01:59:05, brettw wrote:
> Needs copyright.

Acknowledged.

https://codereview.chromium.org/1230293003/diff/20001/tools/gn/bin/roll_gn.py...
tools/gn/bin/roll_gn.py:15: depot_tools_path = None
On 2015/07/15 01:59:05, brettw wrote:
> Can this have some documentation and an example at the top?

I assume "this" means the roll_gn script as a whole, and not this stupid
depot_tools hack :).

Will fix.

[brettw, 2015-07-15 02:43:37]

https://codereview.chromium.org/1230293003/diff/20001/tools/gn/bin/roll_gn.py
File tools/gn/bin/roll_gn.py (right):

https://codereview.chromium.org/1230293003/diff/20001/tools/gn/bin/roll_gn.py...
tools/gn/bin/roll_gn.py:15: depot_tools_path = None
Correct, you can be assured I did not notice the stupid depot tools hack.

[Nico, 2015-07-15 20:24:25]

neat! a few minor comments, all optional

https://codereview.chromium.org/1230293003/diff/20001/tools/gn/bin/roll_gn.py
File tools/gn/bin/roll_gn.py (right):

https://codereview.chromium.org/1230293003/diff/20001/tools/gn/bin/roll_gn.py...
tools/gn/bin/roll_gn.py:24: sys.path.append(depot_tools_path)
nit: always prepend to sys.path, else you can end up with local-env-dependent
stuff winning over the path you want

https://codereview.chromium.org/1230293003/diff/20001/tools/gn/bin/roll_gn.py...
tools/gn/bin/roll_gn.py:85: os.chdir(self.chromium_src_dir)
i always encourage people to make their code not change the cwd (subprocess has
a cwd parameter that you can pass for children, then you don't need to chdir for
subprocesses for example)

https://codereview.chromium.org/1230293003/diff/20001/tools/gn/bin/roll_gn.py...
tools/gn/bin/roll_gn.py:242: fname = 'gn.exe.sha1' if platform == 'win' else
'gn.sha1'
suddenly, 4-space indent?

https://codereview.chromium.org/1230293003/diff/20001/tools/gn/bin/roll_gn.py...
tools/gn/bin/roll_gn.py:342: p = subprocess.Popen(cmd, stdout=subprocess.PIPE,
shell=True)
do you need the shell bit? if not, i'd recommend not using it and instead 
(since it makes things behave differently on win and non-win; for example if cmd
is a list instead of a string non-win will only treat the first entry as command
and the rest as shell params). Oh, I guess you might need it because of the .bat
files in depot_tools. In that case, nevermind.

[Dirk Pranke, 2015-07-15 20:35:57]

https://codereview.chromium.org/1230293003/diff/20001/tools/gn/bin/roll_gn.py
File tools/gn/bin/roll_gn.py (right):

https://codereview.chromium.org/1230293003/diff/20001/tools/gn/bin/roll_gn.py...
tools/gn/bin/roll_gn.py:24: sys.path.append(depot_tools_path)
On 2015/07/15 20:24:25, Nico wrote:
> nit: always prepend to sys.path, else you can end up with local-env-dependent
> stuff winning over the path you want

true.

https://codereview.chromium.org/1230293003/diff/20001/tools/gn/bin/roll_gn.py...
tools/gn/bin/roll_gn.py:85: os.chdir(self.chromium_src_dir)
On 2015/07/15 20:24:25, Nico wrote:
> i always encourage people to make their code not change the cwd (subprocess
has
> a cwd parameter that you can pass for children, then you don't need to chdir
for
> subprocesses for example)

Yeah, I do, too. In this case I was being lazy.

https://codereview.chromium.org/1230293003/diff/20001/tools/gn/bin/roll_gn.py...
tools/gn/bin/roll_gn.py:242: fname = 'gn.exe.sha1' if platform == 'win' else
'gn.sha1'
On 2015/07/15 20:24:25, Nico wrote:
> suddenly, 4-space indent?

bad indent. will fix.

https://codereview.chromium.org/1230293003/diff/20001/tools/gn/bin/roll_gn.py...
tools/gn/bin/roll_gn.py:342: p = subprocess.Popen(cmd, stdout=subprocess.PIPE,
shell=True)
On 2015/07/15 20:24:25, Nico wrote:
> do you need the shell bit? if not, i'd recommend not using it and instead 
> (since it makes things behave differently on win and non-win; for example if
cmd
> is a list instead of a string non-win will only treat the first entry as
command
> and the rest as shell params). Oh, I guess you might need it because of the
.bat
> files in depot_tools. In that case, nevermind.

In many cases, I need shell=True. It is possible to fix the callers, but I'd
just as soon not do that until I decide to put the effort in to make this work
on windows as well.

[Dirk Pranke, 2015-07-17 00:33:51]

The CQ bit was checked by dpranke@chromium.org

[Dirk Pranke, 2015-07-17 00:33:52]

The patchset sent to the CQ was uploaded after l-g-t-m from brettw@chromium.org
Link to the patchset: https://codereview.chromium.org/1230293003/#ps40001
(title: "update w/ review feedback")

[commit-bot: I haz the power, 2015-07-17 00:36:06]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1230293003/40001

[commit-bot: I haz the power, 2015-07-17 00:45:50]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-07-17 00:46:37]

Patchset 3 (id:??) landed as
https://crrev.com/97ec9ac8703dc10eaef5e60984bb3ecdfad344bd
Cr-Commit-Position: refs/heads/master@{#339191}