Add support for smooth scrolling.

See #612.

CHANGELOG.asciidoc

@@ -23,6 +23,7 @@ Added
 - New commands `:message-info`, `:message-error` and `:message-warning` to show messages in the statusbar, e.g. from an userscript.
 - There are now some example userscripts in `misc/userscripts`.
 - New command `:scroll-px` which replaces `:scroll` for pixel-exact scrolling.
+- New setting `ui -> smooth-scrolling`.
 
 Changed
 ~~~~~~~

doc/help/settings.asciidoc

@@ -40,6 +40,7 @@
 |<<ui-frame-flattening,frame-flattening>>|Whether to  expand each subframe to its contents.
 |<<ui-user-stylesheet,user-stylesheet>>|User stylesheet to use (absolute filename or CSS string). Will expand environment variables.
 |<<ui-css-media-type,css-media-type>>|Set the CSS media type.
+|<<ui-smooth-scrolling,smooth-scrolling>>|Whether to enable smooth scrolling for webpages.
 |<<ui-remove-finished-downloads,remove-finished-downloads>>|Whether to remove finished downloads automatically.
 |<<ui-hide-statusbar,hide-statusbar>>|Whether to hide the statusbar unless a message is shown.
 |<<ui-window-title-format,window-title-format>>|The format to use for the window title. The following placeholders are defined:
@@ -531,6 +532,17 @@ Set the CSS media type.
 
 Default: empty
 
+[[ui-smooth-scrolling]]
+=== smooth-scrolling
+Whether to enable smooth scrolling for webpages.
+
+Valid values:
+
+ * +true+
+ * +false+
+
+Default: +pass:[false]+
+
 [[ui-remove-finished-downloads]]
 === remove-finished-downloads
 Whether to remove finished downloads automatically.

qutebrowser/config/configdata.py

@@ -276,6 +276,10 @@ def data(readonly=False):
              SettingValue(typ.String(none_ok=True), ''),
              "Set the CSS media type."),
 
+            ('smooth-scrolling',
+             SettingValue(typ.Bool(), 'false'),
+             "Whether to enable smooth scrolling for webpages."),
+
             ('remove-finished-downloads',
              SettingValue(typ.Bool(), 'false'),
              "Whether to remove finished downloads automatically."),

qutebrowser/config/websettings.py

@@ -322,6 +322,8 @@ MAPPINGS = {
         'css-media-type':
             NullStringSetter(getter=QWebSettings.cssMediaType,
                              setter=QWebSettings.setCSSMediaType),
+        'smooth-scrolling':
+            Attribute(QWebSettings.ScrollAnimatorEnabled),
         #'accelerated-compositing':
         #   Attribute(QWebSettings.AcceleratedCompositingEnabled),
         #'tiled-backing-store':