cc: Make PrepareToDraw return an enum for why it aborts

cc/scheduler/scheduler.h

Index: cc/scheduler/scheduler.h
diff --git a/cc/scheduler/scheduler.h b/cc/scheduler/scheduler.h
index 9209782939068382f106614818d31027b888a26a..34473ad90db7753bfab2bd2e67c4cdc5959fabb6 100644
--- a/cc/scheduler/scheduler.h
+++ b/cc/scheduler/scheduler.h
@@ -13,6 +13,7 @@
 #include "base/time/time.h"
 #include "cc/base/cc_export.h"
 #include "cc/output/begin_frame_args.h"
+#include "cc/scheduler/draw_swap_readback_result.h"
 #include "cc/scheduler/scheduler_settings.h"
 #include "cc/scheduler/scheduler_state_machine.h"
 #include "cc/trees/layer_tree_host.h"
@@ -21,16 +22,6 @@ namespace cc {
 
 class Thread;
 
-struct DrawSwapReadbackResult {
-  DrawSwapReadbackResult()
-      : did_draw(false), did_swap(false), did_readback(false) {}
-  DrawSwapReadbackResult(bool did_draw, bool did_swap, bool did_readback)
-      : did_draw(did_draw), did_swap(did_swap), did_readback(did_readback) {}
-  bool did_draw;
-  bool did_swap;
-  bool did_readback;
-};
-
 class SchedulerClient {
  public:
   virtual void SetNeedsBeginImplFrame(bool enable) = 0;