Avoid over-warning on templatizer props and "static" dynamicFns.

lib/mixins/element-mixin.js

@@ -777,7 +777,10 @@ export const ElementMixin = dedupingMixin(base => {
       // The warning is only enabled in `legacyOptimizations` mode, since
       // we don't want to spam existing users who might have adopted the
       // shorthand when attribute deserialization is not important.
-      if (legacyOptimizations && !(prop in this._properties)) {
+      if (legacyOptimizations && !(prop in this._properties) &&
+          effect.info && effect.info.part && 
+          !(effect.info.part.signature && effect.info.part.signature.static) &&
+          !effect.info.part.hostProp && !templateInfo.nestedTemplate) {
         console.warn(`Property '${prop}' used in template but not declared in 'properties'; ` +
           `attribute will not be observed.`);
       }

lib/mixins/property-effects.js

@@ -2640,7 +2640,7 @@ export const PropertyEffects = dedupingMixin(superClass => {
       let hostProps = nodeInfo.templateInfo.hostProps;
       let mode = '{';
       for (let source in hostProps) {
-        let parts = [{ mode, source, dependencies: [source] }];
+        let parts = [{ mode, source, dependencies: [source], hostProp: true }];
         addBinding(this, templateInfo, nodeInfo, 'property', '_host_' + source, parts);
       }
       return noted;

lib/mixins/template-stamp.js

@@ -204,6 +204,7 @@ export const TemplateStamp = dedupingMixin(
       if (!template._templateInfo) {
         let templateInfo = template._templateInfo = {};
         templateInfo.nodeInfoList = [];
+        templateInfo.nestedTemplate = Boolean(outerTemplateInfo);
         templateInfo.stripWhiteSpace =
           (outerTemplateInfo && outerTemplateInfo.stripWhiteSpace) ||
           template.hasAttribute('strip-whitespace');

test/unit/property-effects.html

@@ -1900,6 +1900,30 @@
     assert.equal(console.warn.callCount, 3);
   });
 
+  test('do not warn on valid non-property bindings', () => {
+    setLegacyOptimizations(true);
+    Polymer({
+      is: 'x-nowarn-undeclared-binding',
+      properties: {
+        hostProp: String
+      },
+      _template: html`
+        <div>[[noDeps()]]</div>
+        <div>[[hostProp]]</div>
+        <template is="dom-repeat" items="[0]" as="instProp">
+          <div>[[instProp]]</div>  <!-- instance prop -->
+          <div>[[hostProp]]</div>  <!-- host prop -->
+          <div>[[noDeps()]]</div>  <!-- method with no deps -->
+        </template>
+      `,
+      noDeps() { return 'static'; }
+    });
+    const el = document.createElement('x-nowarn-undeclared-binding');
+    document.body.appendChild(el);
+    document.body.removeChild(el);
+    assert.equal(console.warn.callCount, 0);
+  });
+
   test('warn when re-declaring a computed property', () => {
     Polymer({
       is: 'x-warn-redeclared-computed',