gpu: Use mojom API for getting video memory usage.

services/ui/gpu/interfaces/gpu_service.mojom

Index: services/ui/gpu/interfaces/gpu_service.mojom
diff --git a/services/ui/gpu/interfaces/gpu_service.mojom b/services/ui/gpu/interfaces/gpu_service.mojom
index d6ca5fce390ee1944c236e8e2e547d2c6b031744..56080ad748c9cd390c68676f113217d5a7e3fd18 100644
--- a/services/ui/gpu/interfaces/gpu_service.mojom
+++ b/services/ui/gpu/interfaces/gpu_service.mojom
@@ -6,6 +6,7 @@ module ui.mojom;
 
 import "cc/ipc/display_compositor.mojom";
 import "gpu/ipc/common/gpu_info.mojom";
+import "gpu/ipc/common/memory_stats.mojom";
 import "gpu/ipc/common/surface_handle.mojom";
 import "gpu/ipc/common/sync_token.mojom";
 import "ui/gfx/geometry/mojo/geometry.mojom";
@@ -31,4 +32,6 @@ interface GpuService {
   DestroyGpuMemoryBuffer(gfx.mojom.GpuMemoryBufferId id,
                          int32 client_id,
                          gpu.mojom.SyncToken sync_token);
+
+  GetVideoMemoryUsageStats() => (gpu.mojom.VideoMemoryUsageStats stats);
 };