cc: Add tile-free software compositing mode.

cc/trees/thread_proxy.cc

Index: cc/trees/thread_proxy.cc
diff --git a/cc/trees/thread_proxy.cc b/cc/trees/thread_proxy.cc
index b6d30bf38bfebd1c176219f494aeb01a3afb5d28..e1249256d981282640b698a520c883e81713f29a 100644
--- a/cc/trees/thread_proxy.cc
+++ b/cc/trees/thread_proxy.cc
@@ -912,6 +912,9 @@ ThreadProxy::ScheduledActionDrawAndSwapInternal(bool forced_draw) {
   bool draw_frame = false;
   bool start_ready_animations = true;
 
+  if (layer_tree_host_impl_->settings().tile_free_software_compositing)
+    frame.cannot_append_tile_draw_quads = true;
+
   if (layer_tree_host_impl_->CanDraw()) {
     // Do not start animations if we skip drawing the frame to avoid
     // checkerboarding.