cc: Make PrepareToDraw return an enum for why it aborts

cc/scheduler/draw_swap_readback_result.h

Index: cc/scheduler/draw_swap_readback_result.h
diff --git a/cc/scheduler/draw_swap_readback_result.h b/cc/scheduler/draw_swap_readback_result.h
new file mode 100644
index 0000000000000000000000000000000000000000..1f60e43a24d95048f88e6f470d96569b2abea222
--- /dev/null
+++ b/cc/scheduler/draw_swap_readback_result.h
@@ -0,0 +1,35 @@
+// Copyright 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CC_SCHEDULER_DRAW_SWAP_READBACK_RESULT_H_
+#define CC_SCHEDULER_DRAW_SWAP_READBACK_RESULT_H_
+
+namespace cc {
+
+struct DrawSwapReadbackResult {
+  enum DrawResult {
+    INVALID_RESULT,
+    DID_DRAW,
+    DRAW_ABORTED_CANT_DRAW,
+    DRAW_ABORTED_NO_TREE,
+    DRAW_ABORTED_NO_RENDERER,
+    DRAW_ABORTED_CHECKERBOARD_ANIMATIONS,
+  };
+
+  DrawSwapReadbackResult()
+      : draw_result(INVALID_RESULT), did_swap(false), did_readback(false) {}
+  DrawSwapReadbackResult(DrawResult draw_result,
+                         bool did_swap,
+                         bool did_readback)
+      : draw_result(draw_result),
+        did_swap(did_swap),
+        did_readback(did_readback) {}
+  DrawResult draw_result;
+  bool did_swap;
+  bool did_readback;
+};
+
+}  // namespace cc
+
+#endif  // CC_SCHEDULER_DRAW_SWAP_READBACK_RESULT_H_