Implement a runtime headless mode for Linux

content/browser/compositor/gpu_process_transport_factory.cc

Index: content/browser/compositor/gpu_process_transport_factory.cc
diff --git a/content/browser/compositor/gpu_process_transport_factory.cc b/content/browser/compositor/gpu_process_transport_factory.cc
index 7d1cf0c2d283a6620d1de210bc8fc8348d66ee4d..8ce7cedc87c1bd7d7a056992f1318a7f09ff4d2b 100644
--- a/content/browser/compositor/gpu_process_transport_factory.cc
+++ b/content/browser/compositor/gpu_process_transport_factory.cc
@@ -196,6 +196,10 @@ GpuProcessTransportFactory::~GpuProcessTransportFactory() {
 std::unique_ptr<cc::SoftwareOutputDevice>
 GpuProcessTransportFactory::CreateSoftwareOutputDevice(
     ui::Compositor* compositor) {
+  base::CommandLine* command_line = base::CommandLine::ForCurrentProcess();
+  if (command_line->HasSwitch(switches::kHeadless))
+    return base::WrapUnique(new cc::SoftwareOutputDevice);
+
 #if defined(USE_AURA)
   if (service_manager::ServiceManagerIsRemote()) {
     NOTREACHED();