Revert of Remove default begin frame sources from the renderer

content/renderer/gpu/render_widget_compositor.cc

Index: content/renderer/gpu/render_widget_compositor.cc
diff --git a/content/renderer/gpu/render_widget_compositor.cc b/content/renderer/gpu/render_widget_compositor.cc
index b5b5f2cfe02ee6effbe4c6eafb9c258fdaa2f9ad..672e2033a84638cd7985f0d34ccd19e01ef5ccf0 100644
--- a/content/renderer/gpu/render_widget_compositor.cc
+++ b/content/renderer/gpu/render_widget_compositor.cc
@@ -244,8 +244,6 @@
   if (settings.use_external_begin_frame_source) {
     params.external_begin_frame_source =
         delegate_->CreateExternalBeginFrameSource();
-  } else {
-    DCHECK(settings.use_output_surface_begin_frame_source);
   }
   params.animation_host = cc::AnimationHost::CreateMainInstance();
 
@@ -438,6 +436,9 @@
 
   // TODO(danakj): Only do this on low end devices.
   settings.create_low_res_tiling = true;
+
+  settings.use_external_begin_frame_source = true;
+
 #else  // defined(OS_ANDROID)
 #if !defined(OS_MACOSX)
   if (ui::ShouldHideScrollbars()) {
@@ -474,15 +475,7 @@
     settings.create_low_res_tiling = true;
   if (cmd.HasSwitch(switches::kDisableLowResTiling))
     settings.create_low_res_tiling = false;
-
-  // TODO(enne): fold external BFS into output surface BFS.
-  if (cmd.HasSwitch(switches::kUseRemoteCompositing)) {
-    settings.use_output_surface_begin_frame_source = true;
-    settings.use_external_begin_frame_source = false;
-  } else {
-    settings.use_output_surface_begin_frame_source = false;
-    settings.use_external_begin_frame_source = true;
-  }
+  settings.use_external_begin_frame_source = true;
 
   if (cmd.HasSwitch(switches::kEnableRGBA4444Textures) &&
       !cmd.HasSwitch(switches::kDisableRGBA4444Textures)) {
@@ -503,6 +496,9 @@
 
   settings.use_cached_picture_raster =
       !cmd.HasSwitch(cc::switches::kDisableCachedPictureRaster);
+
+  if (cmd.HasSwitch(switches::kUseRemoteCompositing))
+    settings.use_external_begin_frame_source = false;
 
   return settings;
 }