cc: Make PrepareToDraw return an enum for why it aborts

cc/trees/thread_proxy.cc

 // Copyright 2011 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.
 
 #include "cc/trees/thread_proxy.h"
 
 #include <string>
 
 #include "base/auto_reset.h"
 #include "base/bind.h"
@@ skipping 1092 matching lines @@
       base::Bind(&ThreadProxy::CreateAndInitializeOutputSurface,
                  main_thread_weak_ptr_));
 }
 
 DrawSwapReadbackResult ThreadProxy::DrawSwapReadbackInternal(
     bool forced_draw,
     bool swap_requested,
     bool readback_requested) {
   TRACE_EVENT_SYNTHETIC_DELAY("cc.DrawAndSwap");
   DrawSwapReadbackResult result;
-  result.did_draw = false;
-  result.did_swap = false;
-  result.did_readback = false;
+
   DCHECK(IsImplThread());
   DCHECK(impl().layer_tree_host_impl.get());
-  if (!impl().layer_tree_host_impl)
-    return result;
-
-  DCHECK(impl().layer_tree_host_impl->renderer());
-  if (!impl().layer_tree_host_impl->renderer())
-    return result;
 
   base::TimeTicks start_time = base::TimeTicks::HighResNow();
   base::TimeDelta draw_duration_estimate = DrawDurationEstimate();
   base::AutoReset<bool> mark_inside(&impl().inside_draw, true);
 
   // Advance our animations.
   base::TimeTicks monotonic_time =
       impl().layer_tree_host_impl->CurrentFrameTimeTicks();
   base::Time wall_clock_time = impl().layer_tree_host_impl->CurrentFrameTime();
 
@@ skipping 20 matching lines @@
   LayerTreeHostImpl::FrameData frame;
   bool draw_frame = false;
 
   if (impl().layer_tree_host_impl->CanDraw() &&
       (!drawing_for_readback || can_do_readback)) {
     // If it is for a readback, make sure we draw the portion being read back.
     gfx::Rect readback_rect;
     if (drawing_for_readback)
       readback_rect = impl().readback_request->rect;
 
-    if (impl().layer_tree_host_impl->PrepareToDraw(&frame, readback_rect) ||
-        forced_draw)
-      draw_frame = true;
+    result.draw_result =
+        impl().layer_tree_host_impl->PrepareToDraw(&frame, readback_rect);
+    draw_frame = forced_draw ||
+                 result.draw_result == DrawSwapReadbackResult::DRAW_SUCCESS;
   }
 
   if (draw_frame) {
     impl().layer_tree_host_impl->DrawLayers(
         &frame, impl().scheduler->LastBeginImplFrameTime());
-    result.did_draw = true;
+    result.draw_result = DrawSwapReadbackResult::DRAW_SUCCESS;
+  } else {
+    DCHECK_NE(DrawSwapReadbackResult::DRAW_SUCCESS, result.draw_result);
   }
   impl().layer_tree_host_impl->DidDrawAllLayers(frame);
 
   bool start_ready_animations = draw_frame;
   impl().layer_tree_host_impl->UpdateAnimationState(start_ready_animations);
 
   // Check for a pending CompositeAndReadback.
   if (drawing_for_readback) {
     DCHECK(!swap_requested);
     result.did_readback = false;
@@ skipping 497 matching lines @@
   impl().commit_to_activate_duration_history.InsertSample(
       base::TimeTicks::HighResNow() - impl().commit_complete_time);
 }
 
 void ThreadProxy::DidManageTiles() {
   DCHECK(IsImplThread());
   impl().scheduler->DidManageTiles();
 }
 
 }  // namespace cc