Reset AudioTimestampValidator upon config change

The validator relies on fields from the AudioDecoderConfig to set
timestamp expectations. When the config changes, simply recreate the
validator with the latest config. 

Neglecting to update the config can lead to incorrect detection of
timestamp gaps, which leads to log spam.

TEST=new unit test
BUG=748751

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: Id2de8d1df4307fda95d924e06ae975a715d7cfe9
Reviewed-on: https://chromium-review.googlesource.com/634509
Reviewed-by: Matthew Wolenetz <[email protected]>
Commit-Queue: Chrome Cunningham <[email protected]>
Cr-Commit-Position: refs/heads/master@{#497569}
5 files changed