Fix unintended usage of Polymer.Base. Replace Polymer.mixin with Object.assign.

lib/legacy/legacy-element-mixin.html

@@ -255,7 +255,10 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
        * @return {Object} Target object that was passed as first argument.
        */
       mixin(target, source) {
-        return Polymer.mixin(target, source);
+        for (let i in source) {
+          target[i] = source[i];
+        }
+        return target;
       }
 
       /**

lib/mixins/element-mixin.html

@@ -186,7 +186,7 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
         flattenProperties({}, ownPropertiesForClass(klass));
         let superCtor = Object.getPrototypeOf(klass.prototype).constructor;
         if (superCtor.prototype instanceof PolymerElement) {
-          klass.__classProperties = Polymer.mixin(
+          klass.__classProperties = Object.assign(
             Object.create(propertiesForClass(superCtor)),
             klass.__classProperties);
         }

lib/mixins/property-effects.html

@@ -25,7 +25,6 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
   'use strict';
 
   const CaseMap = Polymer.CaseMap;
-  const mixin = Polymer.mixin;
 
   // Monotonically increasing unique ID used for de-duping effects triggered
   // from multiple properties in the same turn
@@ -390,8 +389,8 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
     if (computeEffects) {
       let inputProps = changedProps;
       while (runEffects(inst, computeEffects, inputProps, oldProps, hasPaths)) {
-        mixin(oldProps, inst.__dataOld);
-        mixin(changedProps, inst.__dataPending);
+        Object.assign(oldProps, inst.__dataOld);
+        Object.assign(changedProps, inst.__dataPending);
         inputProps = inst.__dataPending;
         inst.__dataPending = null;
       }
@@ -741,7 +740,7 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
       // Merge child _hostProps into this _hostProps
       if (n.templateContent) {
         let templateHostProps = n.templateContent._hostProps;
-        Polymer.Base.mixin(hostProps, templateHostProps);
+        Object.assign(hostProps, templateHostProps);
       }
     }
     return hostProps;

lib/utils/mixin.html

@@ -38,26 +38,6 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
     };
   }
 
-  /**
-   * Copies props from a source object to a target object.
-   *
-   * Note, this method uses a simple `for...in` strategy for enumerating
-   * properties.  To ensure only `ownProperties` are copied from source
-   * to target and that accessor implementations are copied, use `extend`.
-   *
-   * @memberof Polymer
-   * @method mixin
-   * @param {Object} target Target object to copy properties to.
-   * @param {Object} source Source object to copy properties from.
-   * @return {Object} Target object that was passed as first argument.
-   */
-  Polymer.mixin = function(target, source) {
-    for (let i in source) {
-      target[i] = source[i];
-    }
-    return target;
-  };
-
   /**
    * Wraps an ES6 class expression mixin such that the mixin is only applied
    * if it has not already been applied its base argument.  Also memoizes mixin

lib/utils/templatize.html

@@ -230,7 +230,7 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
         // Mix any pre-bound data into __data; no need to flush this to
         // instances since they pull from the template at instance-time
         if (template.__dataProto) {
-          Polymer.mixin(template.__data, template.__dataProto);
+          Object.assign(template.__data, template.__dataProto);
         }
         // Clear any pending data for performance
         template.__dataTemp = {};