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Adds an error log entry to chrome://media-internals when MSE's
MP4 stream parser detects an unfragmented MP4. This error log should
help make it more clear why the parse fails in this unfortunately common
case.

BUG=487410
R=dalecurtis,chcunningham
TEST=Manually verified the log entry occurs for the repro in bug 487410.

Review URL: https://codereview.chromium.org/1147453002

Cr-Commit-Position: refs/heads/master@{#330178}