Hide vertical scrollbar when not needed.

[DanielGibbsNZ]

Currently, the vertical scrollbar is always present, and when there is no need for it (i.e. text does not go past the bottom of the editor) it can look a little messy/out of place (in my opinion). Most text areas only show scrollbars when they are actually needed, and I think this would be a good principle to adopt.

[danyaPostfactum]

+1
@nightwing I think we need to move horizontal scrollbar out of virtual_renderer. We can have scrollbars interface
and implement it using native scrollbars and custom ones (maybe in separate git branch)

Reasons to do it:

• custom scrollbars feature
• necessary for native text d'n'd in WebKit ( It scrolls overflow-x div in Y direction while (native) text selection )
• maybe textarea-like native resizer (for textarea replacement use-cases of ACE)

Will it bring sensible performance issues ?

[nightwing]

@danyaPostfactum +∞
See #869 for some more reasons to do that.
I rather like scrollbars on http://www.typescriptlang.org/Playground/, (except autohiding), but don't have time to work on that for now.

Will it bring sensible performance issues ?

Getting rid of setting scrollleft will only improve performance since it causes sync reflow

As about hiding vertical scrollbar, there's easier way, (i needed to do it for autocomplete popup)

[bobmonteverde]

Been trying to figure out where the option is for this, shocking there is no straightforward way. All I want to do is hide the vertical scrollbar until it is needed. This is how the horizontal one works by default, and make a multi editor environment look much sleeker.

I'm tempted to write a hack-ish solution, but i feel this should be a simple built in flag, which most likely should be on by default.

[nightwing]

added option vScrollBarAlwaysVisible