Mac Overlays: Clear root layer's contents when it is not specified

content/common/gpu/image_transport_surface_overlay_mac.mm

 // Copyright 2015 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 "content/common/gpu/image_transport_surface_overlay_mac.h"
 
 #include <algorithm>
 #include <IOSurface/IOSurface.h>
 #include <OpenGL/CGLRenderers.h>
 #include <OpenGL/CGLTypes.h>
@@ skipping 344 matching lines @@
     // Sort the input planes by z-index, and remove any overlays from the
     // damage rect.
     gfx::RectF dip_damage_rect = ConvertRectToDIPF(
         swap->scale_factor, swap->pixel_damage_rect);
     std::sort(swap->overlay_planes.begin(), swap->overlay_planes.end(),
               OverlayPlane::Compare);
     for (auto& plane : swap->overlay_planes)
       dip_damage_rect.Subtract(plane->dip_frame_rect);
 
     ScopedCAActionDisabler disabler;
-    if (swap->root_plane.get())
-      UpdateRootAndPartialDamagePlanes(swap->root_plane, dip_damage_rect);
+    UpdateRootAndPartialDamagePlanes(swap->root_plane, dip_damage_rect);
     UpdateOverlayPlanes(swap->overlay_planes);
     UpdateCALayerTree();
     swap->overlay_planes.clear();
   }
 
   // Send acknowledgement to the browser.
   GpuHostMsg_AcceleratedSurfaceBuffersSwapped_Params params;
   params.surface_handle =
       ui::SurfaceHandleFromCAContextID([ca_context_ contextId]);
   params.size = swap->pixel_size;
@@ skipping 26 matching lines @@
     old_plane->Destroy();
 }
 
 void ImageTransportSurfaceOverlayMac::UpdateRootAndPartialDamagePlanes(
     const linked_ptr<OverlayPlane>& new_root_plane,
     const gfx::RectF& dip_damage_rect) {
   std::list<linked_ptr<OverlayPlane>> old_partial_damage_planes;
   old_partial_damage_planes.swap(current_partial_damage_planes_);
   linked_ptr<OverlayPlane> plane_for_swap;
 
+  // If there is no new root plane, destroy the old one.
+  if (!new_root_plane.get()) {
+    for (auto& old_plane : old_partial_damage_planes)
+      old_plane->Destroy();
+    if (current_root_plane_.get())
+      current_root_plane_->Destroy();
+    current_root_plane_.reset();
+    return;
+  }
+
   // If the frame's size changed, if we haven't updated the root layer, or if
   // we have full damage, then use the root layer directly.
   if (!current_root_plane_.get() ||
       current_root_plane_->dip_frame_rect != new_root_plane->dip_frame_rect ||
       dip_damage_rect == new_root_plane->dip_frame_rect) {
     plane_for_swap = new_root_plane;
   }
 
   // Walk though the existing partial damage layers and see if there is one that
   // is appropriate to re-use.
@@ skipping 284 matching lines @@
   // Compute the previous vsync time.
   base::TimeTicks previous_vsync =
       vsync_interval_ * ((from - vsync_timebase_) / vsync_interval_) +
       vsync_timebase_;
 
   // Return |interval_fraction| through the next vsync.
   return previous_vsync + (1 + interval_fraction) * vsync_interval_;
 }
 
 }  // namespace content