Revert of Always notify the MediaPlayer of any seek. (https://codereview.chromium.org/431903003/)

Reason for revert:
Test now flakily crashing on all platforms after this change:
http/tests/media/media-source/mediasource-duration.html

http://test-results.appspot.com/dashboards/flakiness_dashboard.html#tests=http%2Ftests%2Fmedia%2Fmedia-source%2Fmediasource-duration.html

Example build: http://build.chromium.org/p/chromium.webkit/builders/WebKit%20Linux/builds/34873

BUG=399523

Original issue's description:
> Always notify the MediaPlayer of any seek.
> 
> This change removes short circuit logic for seeking to the current position.
> There are certain situations, like seeking to a truncated duration, where the
> HTMLMediaElement is not in the best position to determine whether a call to
> the MediaPlayer is necessary or not. This change allows the
> MediaPlayer/WebMediaPlayer implementation to determine what the best course
> of action should be. This also makes the seeking behavior more spec
> compliant because even a seek to the current position should have the
> seeking attribute be true until a stable state occurs. This is guaranteed
> when calling into the MediaPlayer and allows all seeks to be treated the
> same at the HTMLMediaElement level.
> 
> BUG=266631
> TEST=LayoutTests/media/video-seek-to-current-position.html
> 
> Committed: https://src.chromium.org/viewvc/blink?view=rev&revision=179347

TBR=acolwell@chromium.org,philipj@opera.com,srirama.m@samsung.com
NOTREECHECKS=true
NOTRY=true
BUG=266631

Review URL: https://codereview.chromium.org/431273003

git-svn-id: svn://svn.chromium.org/blink/trunk@179368 bbb929c8-8fbe-4397-9dbb-9b2b20218538