Media Controls: Fix time updates when dragging from track not scrubber

Media Controls: Fix time updates when dragging from track not scrubber

The current time displayed by media controls wasn't being updated (by
calling updateCurrentTimeDisplay) whilst dragging the scrubber, if the
drag started from the track (starting in SliderThumbElement::dragFrom)
rather than from the scrubber (starting with a mousedown event handled
by SliderThumbElement::defaultEventHandler).

This was because dragging wasn't being correctly detected (it was
checking sliderThumbElement()->isActive(), but the slider thumb doesn't
get activated in the dragFrom case). Hence dragging detection has been
replaced by robust data from the SliderThumbElement itself.

The SliderThumbElement was also tweaked such that it is not marked as
dragging for the input event generated by SliderThumbElement::dragFrom's
call to setPositionFromPoint, since this movement is the result of the
mousedown on the track, not a mousemove (drag).

This will also be useful for subsequent UMA (https://crbug.com/693630).

BUG=695459

[johnme, 2017-02-23 17:58:45]

The CQ bit was checked by johnme@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2017-02-23 17:59:18]

Dry run: CQ is trying da patch. Follow status at
 
https://chromium-cq-status.appspot.com/v2/patch-status/codereview.chromium.or...

[commit-bot: I haz the power, 2017-02-23 19:44:08]

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

[commit-bot: I haz the power, 2017-02-23 19:44:08]

Dry run: Try jobs failed on following builders:
  win_chromium_rel_ng on master.tryserver.chromium.win (JOB_FAILED,
http://build.chromium.org/p/tryserver.chromium.win/builders/win_chromium_rel_...)

[johnme, 2017-03-08 13:15:34]

Description was changed from

==========
Media Controls: Fix time updates when dragging from track not scrubber

The current time displayed by media controls wasn't being updated (by
calling updateCurrentTimeDisplay) whilst dragging the scrubber, if the
drag started from the track (starting in SliderThumbElement::dragFrom)
rather than from the scrubber (starting with a mousedown event handled
by SliderThumbElement::defaultEventHandler).

This was because dragging wasn't being correctly detected (it was
checking sliderThumbElement()->isActive(), but the slider thumb doesn't
get activated in the dragFrom case). Hence dragging detection has been
replaced by robust data from the SliderThumbElement itself.

The SliderThumbElement was also tweaked such that it is not marked as
dragging for the input event generated by SliderThumbElement::dragFrom's
call to setPositionFromPoint, since this movement is the result of the
mousedown on the track, not a mousemove (drag).

This will also be useful for subsequent UMA (https://crbug.com/693630).

BUG=695459
==========

to

==========
Media Controls: Fix time updates when dragging from track not scrubber

The current time displayed by media controls wasn't being updated (by
calling updateCurrentTimeDisplay) whilst dragging the scrubber, if the
drag started from the track (starting in SliderThumbElement::dragFrom)
rather than from the scrubber (starting with a mousedown event handled
by SliderThumbElement::defaultEventHandler).

This was because dragging wasn't being correctly detected (it was
checking sliderThumbElement()->isActive(), but the slider thumb doesn't
get activated in the dragFrom case). Hence dragging detection has been
replaced by robust data from the SliderThumbElement itself.

The SliderThumbElement was also tweaked such that it is not marked as
dragging for the input event generated by SliderThumbElement::dragFrom's
call to setPositionFromPoint, since this movement is the result of the
mousedown on the track, not a mousemove (drag).

This will also be useful for subsequent UMA (https://crbug.com/693630).

BUG=695459
==========

[johnme, 2017-03-08 13:16:06]

Abandoned in favor of https://codereview.chromium.org/2725893002
(792dd3474f7076b0dc33126a90ba4affbaac2c7f).