WebUI: cr-slider, simplify slider logic by removing |updateValueInstantly| property

|updateValueInstantly| is only used by the display size slider. The property
was passed through settings-slider. This CL moves the |updateValueInstantly|
logic to settings-slider.

The reasoning is that cr-slider had a property |value| that represents the
slider value unless the slider was in a dragging state and
|updateValueInstantly| was false. A new value called |immediateValue_|
was added to always have the correct value even during drag. But this
was only to ultimately stop a value-changed event from being handled
which would update |pref.value|. Instead of having two properties in
cr-slider and one property in settings-slider to store the slider value,
moving the |updateValueInstantly| logic to settings-slider significantly
simplifies the code.

Bug: 902873
Change-Id: I5d5d8771aa8246850bfd9b4926d820180e43c211
Reviewed-on: https://chromium-review.googlesource.com/c/1363642
Commit-Queue: Esmael El-Moslimany <aee@chromium.org>
Reviewed-by: Demetrios Papadopoulos <dpapad@chromium.org>
Cr-Commit-Position: refs/heads/master@{#614530}
6 files changed