Add --headless flag to Windows

headless/app/headless_shell_switches.cc

Index: headless/app/headless_shell_switches.cc
diff --git a/headless/app/headless_shell_switches.cc b/headless/app/headless_shell_switches.cc
index 9cf9baa4e3393b9ba16f1a18461f355b67331e89..7293dd9a53e39daaadc70d00ec0946d7df403410 100644
--- a/headless/app/headless_shell_switches.cc
+++ b/headless/app/headless_shell_switches.cc
@@ -12,6 +12,9 @@ namespace switches {
 // transparent.
 const char kDefaultBackgroundColor[] = "default-background-color";
 
+// Enable chrash reporter for headless.
+const char kEnableCrashReporter[] = "enable-crash-reporter";
+
 // The directory breakpad should store minidumps in.
 const char kCrashDumpsDir[] = "crash-dumps-dir";