MSE: Refine WebM parser unit test MediaLog verification
MSE: Refine WebM parser unit test MediaLog verification

For the approx. 1500 combinations of Opus configurations involved in
each of a couple WebMClusterParserTests, verifies expected MediaLog
sequence for each, rather than just that the set of all logs matches the
union of all expectations. Does this without regressing the tests'
execution time, and allows early detection of failure to prevent test
regression from building tremendous amount of failed expectations state.
Similar state growth, though for otherwise passing tests, is suspected
of causing test crashes on win7 dbg bots in original
http://crrev.com/1300943002#ps40001.

R=xhwang@chromium.org,chcunningham@chromium.org
BUG=524597
TEST=WebMClusterParserTests:
ReadOpusDurationsSimpleBlockAtEndOfCluster, and
PreferOpusDurationsOverBlockDurations

Review URL: https://codereview.chromium.org/1316013002

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#345764}

axinging/chromium-crosswalk,Chilledheart/chromium,Chilledheart/chromium,Chilledheart/chromium,Chilledheart/chromium,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,axinging/chromium-crosswalk,Chilledheart/chromium,Chilledheart/chromium,Chilledheart/chromium,Chilledheart/chromium,Chilledheart/chromium,axinging/chromium-crosswalk,axinging/chromium-crosswalk