android: Migrate old content readback to use async readback (and delegated renderer)

content/browser/android/content_startup_flags.cc

Index: content/browser/android/content_startup_flags.cc
diff --git a/content/browser/android/content_startup_flags.cc b/content/browser/android/content_startup_flags.cc
index 209455db5ef759ea2392fde12c59073886bb1757..0fe9f827f82952070c82ccf6ce6689950861b5f5 100644
--- a/content/browser/android/content_startup_flags.cc
+++ b/content/browser/android/content_startup_flags.cc
@@ -93,6 +93,8 @@ void SetContentCommandLineFlags(int max_render_process_count,
 
   parsed_command_line->AppendSwitch(switches::kUIPrioritizeInGpuProcess);
 
+  parsed_command_line->AppendSwitch(switches::kEnableDelegatedRenderer);
+
   if (!plugin_descriptor.empty()) {
     parsed_command_line->AppendSwitchNative(
       switches::kRegisterPepperPlugins, plugin_descriptor);