Always create a new VideoToolbox session on Mac OS X < 10.10.3.
In some cases, a new configuration is reported as compatible but results
in corruption on Mac OS X < 10.10.3. With this change, new a new decode
session is created for every configuration change.
This change also reduces the number of detected configuration changes by
only considering the last SPS and PPS in each sample, and ignoring them
if they are the same as the previous values.
BUG=501654
Review URL: https://codereview.chromium.org/
1207623002
Cr-Commit-Position: refs/heads/master@{#335810}