There's currently no way to update the deviceScaleFactor using the internal settings in the GTK port.
Besides the WebKitWebSettings not being connected, the GraphicsContext is currently ignoring the deviceScaleFactor setting. This was fixed in Chromium in bug #88136. The test LayoutTests/fast/hidpi/device-scale-factor-paint.html was added there, and is currently failing in the GTK port.
I don't think we need to update the WebKitWebSettings, but simply make the GraphicContext honor the device scale factor property when drawing the WebView, as the Chromium port does in bug #88136.
Created attachment 146250 [details] Patch
CCing Álex and Martin since they're working around this part
Comment on attachment 146250 [details] Patch View in context: https://bugs.webkit.org/attachment.cgi?id=146250&action=review > Source/WebKit/gtk/ChangeLog:9 > + method of the ChromeClientGTk, since it was previously The t in Gtk is upper. I'd remove everything after the comma =).
Created attachment 146289 [details] Patch
Comment on attachment 146289 [details] Patch Clearing flags on attachment: 146289 Committed r119726: <http://trac.webkit.org/changeset/119726>
All reviewed patches have been landed. Closing bug.