Mozart: Directly associate the renderer with the view tree.

services/gfx/compositor/compositor_engine.cc

Index: services/gfx/compositor/compositor_engine.cc
diff --git a/services/gfx/compositor/compositor_engine.cc b/services/gfx/compositor/compositor_engine.cc
index 3e82c4145fdedcdc4b05f5dfb623357575df13e7..17a36c621b5fe0642519e59ebd7eab53efd5cc6f 100644
--- a/services/gfx/compositor/compositor_engine.cc
+++ b/services/gfx/compositor/compositor_engine.cc
@@ -256,6 +256,17 @@ void CompositorEngine::SetRootScene(
   }
 }
 
+void CompositorEngine::ResetRootScene(RendererState* renderer_state) {
+  DCHECK(IsRendererStateRegisteredDebug(renderer_state));
+  DVLOG(1) << "ResetRootScene: renderer=" << renderer_state;
+
+  // Update the root.
+  if (renderer_state->ResetRootScene()) {
+    ScheduleFrameForRenderer(renderer_state,
+                             Scheduler::SchedulingMode::kSnapshot);
+  }
+}
+
 void CompositorEngine::HitTest(
     RendererState* renderer_state,
     mojo::PointPtr point,