GN: Manually search path for Python

GN: Manually search path for Python

This manually searches the path for python rather than executing "cmd" to find it. This saves about 80ms in run time.

Committed: https://crrev.com/30069efcdbf27248a74fcdcf59e4c08df1d75765
Cr-Commit-Position: refs/heads/master@{#360981}

[brettw, 2015-11-21 00:17:59]

brettw@chromium.org changed reviewers:
+ scottmg@chromium.org

[brettw, 2015-11-21 00:18:05]

The CQ bit was checked by brettw@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-11-21 00:19:42]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1462393003/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1462393003/1

[scottmg, 2015-11-21 00:23:35]

lgtm

https://codereview.chromium.org/1462393003/diff/1/tools/gn/setup.cc
File tools/gn/setup.cc (right):

https://codereview.chromium.org/1462393003/diff/1/tools/gn/setup.cc#newcode153
tools/gn/setup.cc:153: const base::char16 kPythonExeName[] = L"python.exe";
Could hoist this out so that the failure case can also use it.

https://codereview.chromium.org/1462393003/diff/1/tools/gn/setup.cc#newcode165
tools/gn/setup.cc:165: DWORD path_length =
::GetEnvironmentVariable(kPathEnvVarName, NULL, 0);
nullptr

https://codereview.chromium.org/1462393003/diff/1/tools/gn/setup.cc#newcode169
tools/gn/setup.cc:169: ::GetEnvironmentVariable(kPathEnvVarName,
full_path.get(), path_length);
DCHECK return value == path_length - 1 maybe.

[brettw, 2015-11-21 00:34:49]

The CQ bit was checked by brettw@chromium.org

[brettw, 2015-11-21 00:34:49]

The patchset sent to the CQ was uploaded after l-g-t-m from scottmg@chromium.org
Link to the patchset: https://codereview.chromium.org/1462393003/#ps20001
(title: " ")

[commit-bot: I haz the power, 2015-11-21 00:37:05]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1462393003/20001
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1462393003/20001

[commit-bot: I haz the power, 2015-11-21 01:36:51]

Committed patchset #2 (id:20001)

[commit-bot: I haz the power, 2015-11-21 01:37:38]

Patchset 2 (id:??) landed as
https://crrev.com/30069efcdbf27248a74fcdcf59e4c08df1d75765
Cr-Commit-Position: refs/heads/master@{#360981}