The self.popen command is used by a bunch of other code under third_party/WebKit a bunch of the calls are using the stdout/stderr in an unsafe manner.
---------------------------
tansell@tansell-z620-l2:/fast/chrome/src$ ack --type=python "popen\(" third_party/WebKit/                                                                                                                           
third_party/WebKit/Tools/Scripts/webkitpy/tool/commands/rebaseline.py
832:        process = self._tool.executive.popen(subprocess_command, stdout=self._tool.executive.PIPE,
995:        process = self._tool.executive.popen(command, stdout=self._tool.executive.PIPE, stderr=self._tool.executive.STDOUT)

third_party/WebKit/Tools/Scripts/webkitpy/common/system/profiler.py
148:        self._perf_process = self._host.executive.popen(cmd)
188:        self._profiler_process = self._host.executive.popen(cmd)
208:        self._profiler_process = self._host.executive.popen(cmd)

third_party/WebKit/Tools/Scripts/webkitpy/common/system/executive_unittest.py
120:        executive.popen(command_line('echo', 1), stdout=executive.PIPE).wait()
126:        executive.popen(args=command_line('echo', 1), stdout=executive.PIPE).wait()

third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/servers/apache_http.py
139:        self._process = self._executive.popen(self._start_cmd)
166:        proc = self._executive.popen([self._port_obj.path_to_apache(),

third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/servers/server_base.py
166:        self._process = self._executive.popen(self._start_cmd,

third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/bisect_test_ordering.py
151:        output = self.executive.popen([path_to_run_webkit_tests, '--child-processes', '1', '--order', 'none', '--no-retry',

third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/base.py
1133:            self._helper = self._executive.popen([helper_path],

third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/server_process.py
140:        self._proc = self._host.executive.popen(self._cmd, stdin=self._host.executive.PIPE,

third_party/WebKit/Tools/Scripts/webkitpy/layout_tests/port/android.py
733:        self._perf_process = self._host.executive.popen(cmd)
946:            self._port.host.executive.popen(self._android_commands.adb_command() + ['shell', MD5SUM_DEVICE_PATH, device_file],
949:            self._port.host.executive.popen(args=['%s_host' % self._md5sum_path, host_file],

third_party/WebKit/Tools/Scripts/webkitpy/w3c/deps_updater.py
167:        proc = self.executive.popen(cmd, stdout=self.executive.PIPE, stderr=self.executive.PIPE)
---------------------------

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/141b51fc2b3a3e6ce3cc4566c42bd20a30b86c21

commit 141b51fc2b3a3e6ce3cc4566c42bd20a30b86c21
Author: tansell <tansell@chromium.org>
Date: Tue May 10 21:55:11 2016

webkitpy: Remove unused _run_command_with_teed_output

This function appears to be unused and it also uses subprocess in an unsafe
manner (see http://crbug.com/610613).

BUG= 610618 
R=jam@chromium.org,qyearsley@chromium.org,dpranke@chromium.org

Review-Url: https://codereview.chromium.org/1961223004
Cr-Commit-Position: refs/heads/master@{#392735}

[modify] https://crrev.com/141b51fc2b3a3e6ce3cc4566c42bd20a30b86c21/third_party/WebKit/Tools/Scripts/webkitpy/common/system/executive.py

Deprecating component:Blink>LayoutTests, to use label Test=Layout instead. Merging these to component:Blink for the Blink rotation to pick up and re-triage as appropriate. 

The next action here would be point 2 in the original post:
 * Change self.popen to be a "call_output" method (like subprocess.check_output) which always uses .communicate

You can't change popen() to be a call method like communicate, the whole point is that it's *not* communicate. I.e., that it doesn't block waiting for the subprocess to exit.

It may be that there are things calling popen that shouldn't be, but I don't think you can eliminate all uses of popen. We need to be able to talk to long-running processes, and I don't know of another way to do that?

This issue has been Available for over a year. If it's no longer important or seems unlikely to be fixed, please consider closing it out. If it is important, please re-triage the issue.

Sorry for the inconvenience if the bug really should have been left as Available.

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

In light of comment 8, going to close this.