Add setPrivate arg to setProperties

lib/mixins/property-effects.html

@@ -1479,11 +1479,14 @@
        *
        * @param {Object} props Bag of one or more key-value pairs whose key is
        *   a property and value is the new value to set for that property.
+       * @param {boolean=} setPrivate When true, any private values set in
+       *   `props` will be set. By default, `setProperties` will not set
+       *   `readOnly: true` root properties.
        * @public
        */
-      setProperties(props) {
+      setProperties(props, setPrivate) {
         for (let path in props) {
-          if (!this.__readOnly || !this.__readOnly[path]) {
+          if (setPrivate || !this.__readOnly || !this.__readOnly[path]) {
             //TODO(kschaaf): explicitly disallow paths in setProperty?
             // wildcard observers currently only pass the first changed path
             // in the `info` object, and you could do some odd things batching

test/unit/property-effects.html

@@ -253,6 +253,36 @@
     assert.equal(el.observerCounts.multipleDepChangeHandler, 1, 'observer not called once');
   });
 
+  test('setProperties does not set readOnly by default', function() {
+    assert.equal(el.observerCounts.valueChanged, 1);
+    assert.equal(el.observerCounts.readonlyvalueChanged, 0);
+    el.setProperties({
+      value: 'shouldChange',
+      nofx: 'shouldChange',
+      readonlyvalue: 'shouldNotChange'
+    });
+    assert.equal(el.value, 'shouldChange');
+    assert.equal(el.nofx, 'shouldChange');
+    assert.equal(el.readonlyvalue, undefined);
+    assert.equal(el.observerCounts.valueChanged, 2);
+    assert.equal(el.observerCounts.readonlyvalueChanged, 0);
+  });
+
+  test('setProperties sets readOnly using `setPrivate` arg', function() {
+    assert.equal(el.observerCounts.valueChanged, 1);
+    assert.equal(el.observerCounts.readonlyvalueChanged, 0);
+    el.setProperties({
+      value: 'shouldChange',
+      nofx: 'shouldChange',
+      readonlyvalue: 'shouldChange'
+    }, true);
+    assert.equal(el.value, 'shouldChange');
+    assert.equal(el.nofx, 'shouldChange');
+    assert.equal(el.readonlyvalue, 'shouldChange');
+    assert.equal(el.observerCounts.valueChanged, 2);
+    assert.equal(el.observerCounts.readonlyvalueChanged, 1);
+  });
+
   test('annotated computed property', function() {
     el.value = 20;
     el.add = 40;