Fix net_unittests when run in a virtualenv.

net/test/python_utils.cc

 // Copyright (c) 2011 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/test/python_utils.h"
 
 #include <memory>
 
 #include "base/base_paths.h"
 #include "base/command_line.h"
 #include "base/environment.h"
 #include "base/files/file_path.h"
 #include "base/files/file_util.h"
 #include "base/lazy_instance.h"
 #include "base/logging.h"
 #include "base/path_service.h"
 #include "base/process/launch.h"
 #include "base/strings/string_util.h"
 #include "base/strings/utf_string_conversions.h"
 
 #if defined(OS_MACOSX)
 #include "base/mac/foundation_util.h"
 #endif
 
 const char kPythonPathEnv[] = "PYTHONPATH";
+const char kPythonVirtualEnv[] = "VIRTUAL_ENV";
 
 void ClearPythonPath() {
   std::unique_ptr<base::Environment> env(base::Environment::Create());
   env->UnSetVar(kPythonPathEnv);
 }
 
 void AppendToPythonPath(const base::FilePath& dir) {
   std::unique_ptr<base::Environment> env(base::Environment::Create());
   std::string old_path;
   std::string dir_path;
@@ skipping 59 matching lines @@
     CHECK(GetAppOutput(command, &output));
     // This does only work if cmd.exe doesn't use a non-US codepage.
     path_ = base::ASCIIToUTF16(output);
     TrimWhitespace(path_, base::TRIM_ALL, &path_);
   }
   base::string16 path_;
 };
 static base::LazyInstance<PythonExePath>::Leaky g_python_path;
 #endif
 
+bool IsInPythonVirtualEnv() {
+  return base::Environment::Create()->HasVar(kPythonVirtualEnv);
+}
+
 bool GetPythonCommand(base::CommandLine* python_cmd) {
   DCHECK(python_cmd);
 
 #if defined(OS_WIN)
   // Most developers have depot_tools in their path, which only has a
   // python.bat, not a python.exe.  Go through cmd to find the path to
   // the python executable.
   // (Don't just return a a "cmd /c python" command line, because then tests
   // that try to kill the python process will kill the cmd process instead,
   // which can cause flakiness.)
   python_cmd->SetProgram(base::FilePath(g_python_path.Get().path_));
 #else
   python_cmd->SetProgram(base::FilePath(FILE_PATH_LITERAL("python")));
 #endif
 
   // Launch python in unbuffered mode, so that python output doesn't mix with
   // gtest output in buildbot log files. See http://crbug.com/147368.
   python_cmd->AppendArg("-u");
 
-  // Prevent using system-installed libraries. Use hermetic versioned copies.
-  python_cmd->AppendArg("-S");
+  if (!IsInPythonVirtualEnv()) {
+    // Prevent using system-installed libraries. Use hermetic versioned copies.
+    python_cmd->AppendArg("-S");
+  }
 
   return true;
 }