Clean up orphaned testserver processes before launching a new one in net::TestServer

Several chrome tests have failed in recent days because some test cases crashed due to failures, leaving behind orphaned testserver processes. These test suites do not use out_of_proc_test_runner, and therefore, do not get the benefit of using the LaunchAppInNewProcessGroup()/KillProcessGroup() mechanism.

This patch implements an added layer of safety, by causing TestServer::LaunchPython() to first kill any remaining orphaned instances of testserver.py before launching a new one. The check for an orphaned testserver process on POSIX is a process with exe_name "python", a parent_pid of "1" (indicating that it's an orphan), and command line parameters that contain the strings "testserver.py" and "<port>" where <port> is the port that is being used by the test server instance.

BUG=55808,57253
TEST=Run a test that spawns a testserver and dies. Run another test. It shouldn't fail.

Review URL: http://codereview.chromium.org/3537002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@61584 0039d316-1c4b-4281-b951-d872f2087c98

• base/process_util.h[diff]
• base/process_util_linux.cc[diff]
• base/process_util_mac.mm[diff]
• net/test/test_server_posix.cc[diff]