Which mobile devices support high accuracy HTML5 geolocation?

Which mobile devices support high accuracy HTML5 geolocation?

I am offering an HTML5 app which provides precise GPS location. I wish to
provide a description of which systems will support this.
I already know they need a phone or tablet which has GPS hardware built in.
What I don't know is which OSes and version will give an HTML5 app the
GPS-level precision. I am concerned that the precision will only be
network level location. We need GPS location so that it will be enough
information to at least get to the correct street block.
So, I expect Android supports this, and iPhone, but do they really give
GPS location to HTML5 apps? Is this widely supported? Preferably, can you
let me know which versions started doing this, and which ones do it
reliably?
Can I depend on HTML5 location as being supported on modern smartphones?