Introduce DisplayProvider for DisplayCompositor.

services/ui/gpu/gpu_main.h

Index: services/ui/gpu/gpu_main.h
diff --git a/services/ui/gpu/gpu_main.h b/services/ui/gpu/gpu_main.h
index 8b8ac01105ba3f34a08aeefdfb43e1e6dc29a2b5..82accf9b3ab6f4d8147252df95de5cb3f32a6c57 100644
--- a/services/ui/gpu/gpu_main.h
+++ b/services/ui/gpu/gpu_main.h
@@ -12,6 +12,7 @@
 #include "services/ui/gpu/interfaces/gpu_main.mojom.h"
 #include "services/ui/gpu/interfaces/gpu_service.mojom.h"
 #include "services/ui/surfaces/display_compositor.h"
+#include "services/ui/surfaces/display_provider.h"
 
 namespace gpu {
 class GpuMemoryBufferFactory;
@@ -84,6 +85,7 @@ class GpuMain : public gpu::GpuSandboxHelper, public mojom::GpuMain {
       pending_display_compositor_client_info_;
 
   std::unique_ptr<DisplayCompositor> display_compositor_;
+  std::unique_ptr<DisplayProvider> display_provider_;
 
   std::unique_ptr<gpu::GpuMemoryBufferFactory> gpu_memory_buffer_factory_;