Part of http://flutter.dev/go/impeller-dart
Umbrella bug #130921.

Implement dart:gpu.DeviceBuffer (use GpuDeviceBuffer if the package migration has not been completed).
When calling context.createTexture, create an impeller::DeviceBuffer backed GpuDeviceBuffer created using the implicit global allocator stored as part of the context (add the allocator to the context if it hasn't been added yet).