Implement a runtime headless mode for Linux

ui/base/ime/input_method_factory.cc

Index: ui/base/ime/input_method_factory.cc
diff --git a/ui/base/ime/input_method_factory.cc b/ui/base/ime/input_method_factory.cc
index f0ed9e28545ca33cff7a2ca5b6043c73c3fbf9e5..e05e51ea5afab3db3a45f175400855e4fa3c9780 100644
--- a/ui/base/ime/input_method_factory.cc
+++ b/ui/base/ime/input_method_factory.cc
@@ -4,9 +4,11 @@
 
 #include "ui/base/ime/input_method_factory.h"
 
+#include "base/command_line.h"
 #include "base/memory/ptr_util.h"
 #include "build/build_config.h"
 #include "ui/base/ime/mock_input_method.h"
+#include "ui/gfx/switches.h"
 
 #if defined(OS_CHROMEOS)
 #include "ui/base/ime/input_method_chromeos.h"
@@ -33,6 +35,13 @@ bool g_create_input_method_called = false;
 }  // namespace
 
 namespace ui {
+namespace {
+
+bool RunningInHeadlessMode() {
+  return base::CommandLine::ForCurrentProcess()->HasSwitch(switches::kHeadless);
+}
+
+}  // namespace
 
 std::unique_ptr<InputMethod> CreateInputMethod(
     internal::InputMethodDelegate* delegate,
@@ -49,6 +58,9 @@ std::unique_ptr<InputMethod> CreateInputMethod(
   if (g_input_method_set_for_testing)
     return base::MakeUnique<MockInputMethod>(delegate);
 
+  if (RunningInHeadlessMode())
+    return base::WrapUnique(new MockInputMethod(delegate));
+
 #if defined(OS_CHROMEOS)
   return base::MakeUnique<InputMethodChromeOS>(delegate);
 #elif defined(OS_WIN)