Remove WebMediaSourceNew declaration.
Remove WebMediaSourceNew declaration.

BUG=272993
TEST=All existing LayoutTests still pass.

Review URL: https://chromiumcodereview.appspot.com/23658043

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@157720 bbb929c8-8fbe-4397-9dbb-9b2b20218538

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