Allow setting unknown CSS properties, e.g. CSS variables

tools/dom/scripts/css_code_generator.py

 #!/usr/bin/python
 #
 # Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 """Generates CSSStyleDeclaration template file from css property definitions
 defined in WebKit."""
 
 import tempfile, os, re
@@ skipping 101 matching lines @@
     return style;
   }
 
   /// Returns the value of the property if the provided *CSS* property
   /// name is supported on this element and if the value is set. Otherwise
   /// returns an empty string.
   ///
   /// Please note the property name uses camelCase, not-hyphens.
   String getPropertyValue(String propertyName) {
     var propValue = _getPropertyValueHelper(propertyName);
-    return propValue != null ? propValue : '';
+    return propValue ?? '';
   }
 
   String _getPropertyValueHelper(String propertyName) {
-    if (_supportsProperty(_camelCase(propertyName))) {
-      return _getPropertyValue(propertyName);
-    } else {
-      return _getPropertyValue(Device.cssPrefix + propertyName);
-    }
+    return _getPropertyValue(_browserPropertyName(propertyName));
   }
 
   /**
    * Returns true if the provided *CSS* property name is supported on this
    * element.
    *
    * Please note the property name camelCase, not-hyphens. This
    * method returns true if the property is accessible via an unprefixed _or_
    * prefixed property.
    */
   bool supportsProperty(String propertyName) {
     return _supportsProperty(propertyName) ||
-        _supportsProperty(_camelCase(Device.cssPrefix + propertyName));
+        _supportsProperty(_camelCase("${Device.cssPrefix}$propertyName"));
   }
 
   bool _supportsProperty(String propertyName) {
 $if DART2JS
     return JS('bool', '# in #', propertyName, this);
 $else
     // You can't just check the value of a property, because there is no way
     // to distinguish between property not being present in the browser and
     // not having a value at all. (Ultimately we'll want the native method to
     // return null if the property doesn't exist and empty string if it's
     // defined but just doesn't have a value.
     return _hasProperty(propertyName);
 $endif
   }
 
 $if DARTIUM
   bool _hasProperty(String propertyName) =>
       _blink.BlinkCSSStyleDeclaration.instance.$__get___propertyIsEnumerable_Callback_1_(this, propertyName);
 $endif
 
   @DomName('CSSStyleDeclaration.setProperty')
   void setProperty(String propertyName, String value, [String priority]) {
     return _setPropertyHelper(_browserPropertyName(propertyName),
       value, priority);
   }
 
   String _browserPropertyName(String propertyName) {
     String name = _readCache(propertyName);
     if (name is String) return name;
-    if (_supportsProperty(_camelCase(propertyName))) {
-      name = propertyName;
-    } else {
-      name = Device.cssPrefix + propertyName;
-    }
+    name = _supportedBrowserPropertyName(propertyName);
     _writeCache(propertyName, name);
     return name;
   }
 
+  String _supportedBrowserPropertyName(String propertyName) {
+    if (_supportsProperty(_camelCase(propertyName))) {
+      return propertyName;
+    }
+    var prefixed = "${Device.cssPrefix}$propertyName";
+    if (_supportsProperty(prefixed)) {
+      return prefixed;
+    }
+    // May be a CSS variable, just use it as provided.
+    return propertyName;
+  }
+
 $if DART2JS
   static final _propertyCache = JS('', '{}');
   static String _readCache(String key) =>
     JS('String|Null', '#[#]', _propertyCache, key);
   static void _writeCache(String key, String value) {
     JS('void', '#[#] = #', _propertyCache, key, value);
   }
 $else
   static String _readCache(String key) => null;
   static void _writeCache(String key, value) {}
@@ skipping 164 matching lines @@
       class_lines.append(annotated[base_css_name])
     class_lines.append("""
   set %s(String value) {
     setProperty('%s', value, '');
   }
 """ % (camel_case_name, css_name))
 
   class_file.write(''.join(class_lines));
   class_file.write('}\n')
   class_file.close()