Ensure media's buffered ranges always have a range that includes currentTime.
Avoids buffering bar disappearing/reappearing when the bytes are distributed
unevenly throughout the media.

BUG=133567,131444

Review URL: https://chromiumcodereview.appspot.com/10581050

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@143765 0039d316-1c4b-4281-b951-d872f2087c98
19 files changed