Revert of Update SourceBufferStream and its unit tests to always expect valid durations.

Revert of Update SourceBufferStream and its unit tests to always expect valid durations. (https://codereview.chromium.org/379693002/)

Reason for revert:
This seems to have broken several layout tests:

event-attributes.html 
media-controller-time-clamp.html 
video-currentTime-delay.html 
video-currentTime-set.html 
video-duration-known-after-eos.html 
video-loop.html 
video-playbackrate.html 
video-played-collapse.html 
video-seek-past-end-paused.html 
video-seek-past-end-playing.html 
video-seek-to-duration-with-playbackrate-zero.html 

See for example this build:
http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Mac10.6%20(dbg)/builds/16392

Original issue's description:
> Update SourceBufferStream and its unit tests to always expect valid durations.
> 
> This change fixes the SourceBufferStream unit tests so that they always
> provide valid durations for buffers that it passes to SourceBufferStream.
> I've also added code to SoureBufferStream to verify that it always gets
> buffers with valid durations.
> 
> Minor tweaks to test expectations were needed to compensate for the
> SourceBufferStream behaving differently when it got actual durations instead
> of using the durations it made up. In most cases I just used the duration
> the SourceBufferStream was ultimately using. In a few cases the duration
> the SourceBufferStream was generating didn't make any sense so I simply
> changed the expectations to match the new behavior.
> 
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=283365

TBR=wolenetz@chromium.org,dalecurtis@chromium.org,acolwell@chromium.org
NOTREECHECKS=true
NOTRY=true

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=283390

[falken, 2014-07-16 08:55:13]

Created Revert of Update SourceBufferStream and its unit tests to always expect
valid durations.

[commit-bot: I haz the power, 2014-07-16 08:57:31]

CQ is trying da patch. Follow status at
 https://chromium-status.appspot.com/cq/falken@chromium.org/392193003/1

[commit-bot: I haz the power, 2014-07-16 08:59:30]

Change committed as 283390