Move buffer from extend_and_predict into TileWorkerData

This avoids unneeded initializations.

extend_and_predict is called from multiple nested loops, allocate
large buffer on stack and use just a portion of it.
-ftrivial-auto-var-init= inserts initializations which performed on
multiple iterations of loops causing 258.5% regression on
webrtc_perf_tests decode_time/pc_vp9svc_3sl_low_alice-video.

Bug: 1020220, 977230

Change-Id: I7e5bb3c3780adab74dd8b5c8bd2a96bf45e0c231
2 files changed