mus: Simplify generation of memory-buffer ids.

services/ui/common/mus_gpu_memory_buffer_manager.h

Index: services/ui/common/mus_gpu_memory_buffer_manager.h
diff --git a/services/ui/common/mus_gpu_memory_buffer_manager.h b/services/ui/common/mus_gpu_memory_buffer_manager.h
index cb1bd850c3b0a067f4de82047e138399fc5f0c0e..768e1c971939ff7825a77ad1a440e8db4b21cb85 100644
--- a/services/ui/common/mus_gpu_memory_buffer_manager.h
+++ b/services/ui/common/mus_gpu_memory_buffer_manager.h
@@ -9,6 +9,7 @@
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
+#include "base/threading/thread_checker.h"
 #include "gpu/command_buffer/client/gpu_memory_buffer_manager.h"
 #include "services/ui/gpu/interfaces/gpu_service_internal.mojom.h"
 
@@ -16,7 +17,8 @@ namespace ui {
 
 // This GpuMemoryBufferManager is for establishing a GpuChannelHost used by
 // mus locally.
-class MusGpuMemoryBufferManager : public gpu::GpuMemoryBufferManager {
+class MusGpuMemoryBufferManager : public gpu::GpuMemoryBufferManager,
+                                  public base::ThreadChecker {
  public:
   MusGpuMemoryBufferManager(mojom::GpuServiceInternal* gpu_service,
                             int client_id);
@@ -44,6 +46,7 @@ class MusGpuMemoryBufferManager : public gpu::GpuMemoryBufferManager {
   mojom::GpuServiceInternal* gpu_service_;
 
   const int client_id_;
+  int next_gpu_memory_id_ = 1;
   base::WeakPtrFactory<MusGpuMemoryBufferManager> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(MusGpuMemoryBufferManager);