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When updating the ReadyState, HTMLMediaElement will immediately check the duration.
If at that time has_valid_metadata_ is false, we will return NaN.
So the has_valid_metadata_ has to be set before ReadyState is updated.

BUG=414499

Review URL: https://codereview.chromium.org/572803002

Cr-Commit-Position: refs/heads/master@{#294979}