Always force swap for SurfaceDisplayOutputSurface.

Force reclaim clears out the Surface's copy of the delegated frame, so a swap is always necessary to restore its contents.

Review URL: https://codereview.chromium.org/886633007

Cr-Commit-Position: refs/heads/master@{#314492}

cc/surfaces/surface_display_output_surface.cc

@@ -25,6 +25,9 @@ SurfaceDisplayOutputSurface::SurfaceDisplayOutputSurface(
   capabilities_.delegated_rendering = true;
   capabilities_.max_frames_pending = 1;
   capabilities_.can_force_reclaim_resources = true;
+  // Frame always needs to be swapped because forced resource reclaiming
+  // destroys the Display's copy.
+  capabilities_.draw_and_swap_full_viewport_every_frame = true;
 }
 
 SurfaceDisplayOutputSurface::~SurfaceDisplayOutputSurface() {

cc/trees/layer_tree_host_impl.cc

@@ -675,6 +675,7 @@ DrawResult LayerTreeHostImpl::CalculateRenderPasses(
   if (root_surface_has_contributing_layers &&
       root_surface_has_no_visible_damage &&
       active_tree_->LayersWithCopyOutputRequest().empty() &&
+      !output_surface_->capabilities().can_force_reclaim_resources &&
       !hud_wants_to_draw_) {
     TRACE_EVENT0("cc",
                  "LayerTreeHostImpl::CalculateRenderPasses::EmptyDamageRect");