Add settings to enable/disable CSS regions.

See #612.

CHANGELOG.asciidoc

@@ -25,6 +25,7 @@ Added
 - New command `:scroll-px` which replaces `:scroll` for pixel-exact scrolling.
 - New setting `ui -> smooth-scrolling`.
 - New setting `content -> webgl` to enable/disable https://www.khronos.org/webgl/[WebGL].
+- New setting `content -> css-regions` to enable/disable support for http://dev.w3.org/csswg/css-regions/[CSS Regions].
 
 Changed
 ~~~~~~~

doc/help/settings.asciidoc

@@ -136,6 +136,7 @@
 |<<content-allow-javascript,allow-javascript>>|Enables or disables the running of JavaScript programs.
 |<<content-allow-plugins,allow-plugins>>|Enables or disables plugins in Web pages.
 |<<content-webgl,webgl>>|Enables or disables WebGL.
+|<<content-css-regions,css-regions>>|Enable or disable support for CSS regions.
 |<<content-geolocation,geolocation>>|Allow websites to request geolocations.
 |<<content-notifications,notifications>>|Allow websites to show notifications.
 |<<content-javascript-can-open-windows,javascript-can-open-windows>>|Whether JavaScript programs can open new windows.
@@ -1162,6 +1163,17 @@ Valid values:
 
 Default: +pass:[true]+
 
+[[content-css-regions]]
+=== css-regions
+Enable or disable support for CSS regions.
+
+Valid values:
+
+ * +true+
+ * +false+
+
+Default: +pass:[true]+
+
 [[content-geolocation]]
 === geolocation
 Allow websites to request geolocations.

qutebrowser/config/configdata.py

@@ -613,6 +613,10 @@ def data(readonly=False):
              SettingValue(typ.Bool(), 'true'),
              "Enables or disables WebGL."),
 
+            ('css-regions',
+             SettingValue(typ.Bool(), 'true'),
+             "Enable or disable support for CSS regions."),
+
             ('geolocation',
              SettingValue(typ.BoolAsk(), 'ask'),
              "Allow websites to request geolocations."),

qutebrowser/config/websettings.py

@@ -256,6 +256,8 @@ MAPPINGS = {
             Attribute(QWebSettings.PluginsEnabled),
         'webgl':
             Attribute(QWebSettings.WebGLEnabled),
+        'css-regions':
+            Attribute(QWebSettings.CSSRegionsEnabled),
         'local-content-can-access-remote-urls':
             Attribute(QWebSettings.LocalContentCanAccessRemoteUrls),
         'local-content-can-access-file-urls':