Use CHROME_LOG_FILE environment variable for headless chrome logging

headless/lib/headless_content_main_delegate.cc

 // Copyright 2015 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 "headless/lib/headless_content_main_delegate.h"
 
 #include "base/base_switches.h"
 #include "base/command_line.h"
+#include "base/environment.h"
 #include "base/files/file_util.h"
 #include "base/lazy_instance.h"
 #include "base/path_service.h"
 #include "base/run_loop.h"
 #include "base/strings/string_number_conversions.h"
 #include "base/trace_event/trace_event.h"
 #include "components/crash/content/app/breakpad_linux.h"
 #include "content/public/browser/browser_main_runner.h"
 #include "content/public/common/content_switches.h"
 #include "headless/lib/browser/headless_browser_impl.h"
@@ skipping 101 matching lines @@
 
   base::FilePath log_path;
   logging::LoggingSettings settings;
 
   if (PathService::Get(base::DIR_MODULE, &log_path)) {
     log_path = log_path.Append(log_filename);
   } else {
     log_path = log_filename;
   }
 
+  std::string filename;
+  std::unique_ptr<base::Environment> env(base::Environment::Create());
+  if (env->HasVar("CHROME_LOG_FILE") &&

[Sami, 2017/03/08 10:38:14]

nit: no need to call HasVar since GetVar will just return false if the variable
isn't there.

[irisu, 2017/03/08 23:56:08]

Done.

+      env->GetVar("CHROME_LOG_FILE", &filename) && !filename.empty()) {

[Sami, 2017/03/08 10:38:13]

Could you make this a named constant at the top of this file (e.g., like here:
https://cs.chromium.org/chromium/src/chrome/common/env_vars.cc?rcl=ae2ff2acd1...)

[irisu, 2017/03/08 23:56:08]

Done.

+    log_path = base::FilePath::FromUTF8Unsafe(filename);
+  }
+
   const std::string process_type =
       command_line.GetSwitchValueASCII(switches::kProcessType);
 
   settings.logging_dest = log_mode;
   settings.log_file = log_path.value().c_str();
   settings.lock_log = logging::DONT_LOCK_LOG_FILE;
   settings.delete_old = process_type.empty() ? logging::DELETE_OLD_LOG_FILE
                                              : logging::APPEND_TO_OLD_LOG_FILE;
   bool success = logging::InitLogging(settings);
   DCHECK(success);
@@ skipping 110 matching lines @@
 #endif
 }
 
 content::ContentBrowserClient*
 HeadlessContentMainDelegate::CreateContentBrowserClient() {
   browser_client_.reset(new HeadlessContentBrowserClient(browser_.get()));
   return browser_client_.get();
 }
 
 }  // namespace headless