Add more track buffer logging to SourceBufferStream.
Add more track buffer logging to SourceBufferStream.

Track buffer state is useful for debugging issues with MSE playback
when players append media who's timeline overlaps that of previous
appends.

BUG=spawned from discussion of internal b/23015270

Review URL: https://codereview.chromium.org/1273123003

Cr-Commit-Position: 972c6d2dc6dd5efdad1377c0d224e03eb8f276f7@{#342915}

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