[headless] Normalize log path before passing it on.

Having non canonical forward slashes in log file name causes problems
with sanbox file name pattern handlign on Windows.

Bug: 859676
Change-Id: I8e00eb72db3bd7959b7e8d493fa90c5069727ec3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2518879
Commit-Queue: Peter Kvitek <kvitekp@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Cr-Commit-Position: refs/heads/master@{#823895}

headless/lib/headless_content_main_delegate.cc

@@ -309,6 +309,10 @@ void HeadlessContentMainDelegate::InitLogging(
     log_path = base::FilePath::FromUTF8Unsafe(filename);
   }
 
+  // On Windows, having non canonical forward slashes in log file name causes
+  // problems with sandbox filters, see https://crbug.com/859676
+  log_path = log_path.NormalizePathSeparators();
+
   settings.logging_dest = log_mode;
   settings.log_file_path = log_path.value().c_str();
   settings.lock_log = logging::DONT_LOCK_LOG_FILE;
@@ -318,7 +322,6 @@ void HeadlessContentMainDelegate::InitLogging(
   DCHECK(success);
 }
 
-
 void HeadlessContentMainDelegate::InitCrashReporter(
     const base::CommandLine& command_line) {
   if (command_line.HasSwitch(::switches::kDisableBreakpad))