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This is a reland of daa348fa

Original change's description:
> Attach UsbContext to libusb_device(_handle) pointers
> 
> This change modifies ScopedLibusbDeviceRef and adds a new class
> ScopedLibusbDeviceHandle. This now explicitly own a reference to the
> UsbContext object (which reference counts a libusb_context) in addition
> to the libusb_device or libusb_device_handle they are wrapping.
> 
> This resolves potential use-after-frees possible when posting tasks
> with a ScopedLibusbDeviceRef since the UsbService the task is being
> posted to could be destroyed before the task is executed. The
> libusb_device would then be released after its libusb_context has been
> destroyed.
> 
> This is based on https://crrev.com/c/1131949 after I realized there
> where additional issues that needed to be addressed.
> 
> Bug: 838947
> Change-Id: Idee02828bf615bd477033e585fffe03cf4d20595
> Reviewed-on: https://chromium-review.googlesource.com/1145910
> Reviewed-by: Ken Rockot <rockot@chromium.org>
> Commit-Queue: Reilly Grant <reillyg@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#577329}

Bug: 838947
Change-Id: Ibb916b6dea86f05f0b6d2fdfa2d3b71f8c1e8c66
Reviewed-on: https://chromium-review.googlesource.com/1158770
Commit-Queue: Reilly Grant <reillyg@chromium.org>
Reviewed-by: Matt Reynolds <mattreynolds@chromium.org>
Cr-Commit-Position: refs/heads/master@{#581997}