Remove propertyNameForAttribute since it's never needed.

lib/mixins/element-mixin.html

@@ -545,29 +545,6 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
         }
       }
 
-      /**
-       * Provides a default implementation of the standard Custom Elements
-       * `attributeChangedCallback`.
-       *
-       * By default, attributes declared in `properties` metadata are
-       * deserialized using their `type` information to properties of the
-       * same name.  "Dash-cased" attributes are deserialized to "camelCase"
-       * properties.
-       *
-       * @param {string} name Name of attribute.
-       * @param {?string} old Old value of attribute.
-       * @param {?string} value Current value of attribute.
-       * @override
-       */
-      attributeChangedCallback(name, old, value) {
-        if (old !== value) {
-          let property = this.constructor.propertyNameForAttribute(name);
-          if (!this._hasReadOnlyEffect(property)) {
-            super.attributeChangedCallback(name, old, value);
-          }
-        }
-      }
-
       /**
        * When using the ShadyCSS scoping and custom property shim, causes all
        * shimmed styles in this element (and its subtree) to be updated

lib/mixins/properties-changed.html

@@ -68,21 +68,6 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
           }
         }
 
-        /**
-         * Returns a property name that corresponds to the given attribute.
-         * The attribute name is always lowercase and the property name is the
-         * cased version for which a property accessor was created. Override to
-         * customize this mapping.
-         * @param {string} attribute Attribute to convert
-         * @return {string} Property name corresponding to the given attribute.
-         *
-         * @protected
-         */
-        static propertyNameForAttribute(attribute) {
-          const map = this.prototype.__dataAttributes;
-          return map && map[attribute] || attribute;
-        }
-
         /**
          * Returns an attribute name that corresponds to the given property.
          * The attribute name is the lowercased property name. Override to
@@ -401,7 +386,8 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
          */
         _attributeToProperty(attribute, value, type) {
           if (!this.__serializing) {
-            const property = this.constructor.propertyNameForAttribute(attribute);
+            const map = this.__dataAttributes;
+            const property = map && map[attribute] || attribute;
             this[property] = this._deserializeValue(value, type ||
               this.constructor.typeForProperty(property));
           }

lib/mixins/property-accessors.html

@@ -125,18 +125,6 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
         }
       }
 
-      /**
-       * Returns a property name that corresponds to the given attribute.
-       * By default, converts dash to camel case, e.g. `foo-bar` to `fooBar`.
-       * @param {string} attribute Attribute to convert
-       * @return {string} Property name corresponding to the given attribute.
-       *
-       * @protected
-       */
-      static propertyNameForAttribute(attribute) {
-        return caseMap.dashToCamelCase(attribute);
-      }
-
       /**
        * Returns an attribute name that corresponds to the given property.
        * By default, converts camel to dash case, e.g. `fooBar` to `foo-bar`.