vavda use InputBuffer and VaapiPicture as unique_ptr

This CL teaches vaapi files to treat InputBuffers and VaapiPictures
as move-only unique_ptr, and not as linked_ptr: the latter is been
deprecated now that we have move-only support in STL containers [1].

Only actual code change is in VaVDA::AssignPictureBuffers() where
 picture->Allocate()
is moved to before
 pictures_.insert(..std::move(picture)...).

[1] https://cs.chromium.org/chromium/src/base/memory/linked_ptr.h?type=cs&sq=package:chromium&l=72

Bug: 717265, 556939

TEST=compiled-run chrome and vda unittests [2] on soraka.
Things working as on ToT, no regression in the produced
values observed.

[2] /tmp/video_decode_accelerator_unittest --test_video_data=test-25fps.vp9:320:240:250:250:35:150:12

Cq-Include-Trybots: master.tryserver.chromium.android:android_optional_gpu_tests_rel;master.tryserver.chromium.linux:linux_optional_gpu_tests_rel;master.tryserver.chromium.mac:mac_optional_gpu_tests_rel;master.tryserver.chromium.win:win_optional_gpu_tests_rel
Change-Id: I5e2840a22ec961a437405f43d83207301d5a95bc
Reviewed-on: https://chromium-review.googlesource.com/775815
Reviewed-by: Kuang-che Wu <kcwu@chromium.org>
Commit-Queue: Miguel Casas <mcasas@chromium.org>
Cr-Commit-Position: refs/heads/master@{#518113}
6 files changed