Implement a runtime headless mode for Linux

content/browser/zygote_host/zygote_communication_linux.cc

Index: content/browser/zygote_host/zygote_communication_linux.cc
diff --git a/content/browser/zygote_host/zygote_communication_linux.cc b/content/browser/zygote_host/zygote_communication_linux.cc
index c72bdaf3f5f153de8e22cd56484f089611959d05..475548254a5e554a3b29597e7fe392f6ce932625 100644
--- a/content/browser/zygote_host/zygote_communication_linux.cc
+++ b/content/browser/zygote_host/zygote_communication_linux.cc
@@ -23,6 +23,7 @@
 #include "content/public/common/content_switches.h"
 #include "content/public/common/result_codes.h"
 #include "ui/display/display_switches.h"
+#include "ui/gfx/switches.h"
 
 namespace content {
 
@@ -252,6 +253,9 @@ void ZygoteCommunication::Init() {
       switches::kDisableSeccompFilterSandbox,
       switches::kEnableHeapProfiling,
       switches::kEnableLogging,  // Support, e.g., --enable-logging=stderr.
+      // Need to tell the zygote that it is headless so that we don't try to use
+      // the wrong type of main delegate.
+      switches::kHeadless,
       // Zygote process needs to know what resources to have loaded when it
       // becomes a renderer process.
       switches::kForceDeviceScaleFactor, switches::kLoggingLevel,