Revert "If duration of media source is unknown then return NaN."

Revert "If duration of media source is unknown then return NaN."

This reverts commit 536be704e6ff71001c7f402e18956204bf76f8bf.

Revert "Fix an issue that video is not seekable"

This reverts commit 21f1f757864d7ec360ee1c7a00a6cb31d7af1231.

The first causes the tough_video_cases benchmark to hang and the
second depends on it. Details in bug.

BUG=412897
TBR=qinmin@chromium.org

Committed: https://crrev.com/7e63a0151fb0026af444b31332de4fd293f6fb1d
Cr-Commit-Position: refs/heads/master@{#295282}

[tonyg, 2014-09-17 03:39:16]

The CQ bit was checked by tonyg@chromium.org

[commit-bot: I haz the power, 2014-09-17 03:39:35]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/580673002/1

[commit-bot: I haz the power, 2014-09-17 03:42:55]

The CQ bit was unchecked by commit-bot@chromium.org

[commit-bot: I haz the power, 2014-09-17 03:42:56]

Try jobs failed on following builders:
  mac_gpu on tryserver.chromium.gpu
(http://build.chromium.org/p/tryserver.chromium.gpu/builders/mac_gpu/builds/56927)
  android_aosp on tryserver.chromium.linux
(http://build.chromium.org/p/tryserver.chromium.linux/builders/android_aosp/bu...)
  ios_dbg_simulator on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_dbg_simulator...)
  ios_rel_device on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device/bu...)
  ios_rel_device_ninja on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/ios_rel_device_ni...)
  mac_chromium_compile_dbg on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_comp...)
  mac_chromium_rel_swarming on tryserver.chromium.mac
(http://build.chromium.org/p/tryserver.chromium.mac/builders/mac_chromium_rel_...)
  win8_chromium_rel on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win8_chromium_rel...)
  win_chromium_x64_rel_swarming on tryserver.chromium.win
(http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_x64_...)

[tonyg, 2014-09-17 14:59:37]

The CQ bit was checked by tonyg@chromium.org

[commit-bot: I haz the power, 2014-09-17 14:59:42]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patchset/580673002/20001

[commit-bot: I haz the power, 2014-09-17 15:56:04]

Committed patchset #2 (id:20001) as 5f3af9a2fe6a475392e54bd5af548a59feedb307

[commit-bot: I haz the power, 2014-09-17 15:56:45]

Patchset 2 (id:??) landed as
https://crrev.com/7e63a0151fb0026af444b31332de4fd293f6fb1d
Cr-Commit-Position: refs/heads/master@{#295282}