Don't create private setter for computed properties. Fixes #2016.

src/lib/bind/accessors.html

@@ -169,8 +169,13 @@ subject to an additional IP rights grant found at http://polymer.github.io/PATEN
       // ReadOnly properties have a private setter only
       // TODO(kschaaf): Per current Bind factoring, we shouldn't
       // be interrogating the prototype here
-      if (model.getPropertyInfo && model.getPropertyInfo(property).readOnly) {
-        model['_set' + this.upper(property)] = setter;
+      var info = model.getPropertyInfo && model.getPropertyInfo(property);
+      if (info.readOnly) {
+        // Computed properties are read-only (no property setter), but also don't
+        // need a private setter since they should not be called by the user
+        if (!info.computed) {
+          model['_set' + this.upper(property)] = setter;
+        }
       } else {
         defun.set = setter;
       }

test/unit/bind-elements.html

@@ -58,7 +58,9 @@
         computednotifyingvalue: {
           type: Number,
           notify: true,
-          computed: 'computeNotifyingValue(notifyingvalue)'
+          // Naming here is to test that a private setter is not created for
+          // computed properties
+          computed: '_setComputednotifyingvalue(notifyingvalue)'
         },
         computedFromMultipleValues: {
           type: Number,
@@ -172,7 +174,7 @@
       notifierWithoutComputingChanged: function() {
         this.observerCounts.notifierWithoutComputingChanged++;
       },
-      computeNotifyingValue: function(val) {
+      _setComputednotifyingvalue: function(val) {
         return val + 2;
       },
       computeFromMultipleValues: function(sum1, sum2, divide) {