Explicitly making an element's _template falsy is now considered an…

… allowable setting. This means the element stamps no content, doesn't collect any styles, and avoids looking up a dom-module. This helps address #2708 and the 5 elements Polymer registers that have no template have been set with `_template: null`.

src/lib/custom-style.html

@@ -82,6 +82,7 @@
 
     is: 'custom-style',
     extends: 'style',
+    _template: null,
 
     properties: {
       // include is a property so that it deserializes

src/lib/template/array-selector.html

@@ -66,6 +66,7 @@
 
   Polymer({
     is: 'array-selector',
+    _template: null,
 
     properties: {
 

src/lib/template/dom-bind.html

@@ -62,6 +62,7 @@
     is: 'dom-bind',
 
     extends: 'template',
+    _template: null,
 
     created: function() {
       // Ensure dom-bind doesn't stamp until all possible dependencies

src/lib/template/dom-if.html

@@ -28,6 +28,7 @@
 
     is: 'dom-if',
     extends: 'template',
+    _template: null,
 
     /**
      * Fired whenever DOM is added or removed/hidden by this template (by

src/lib/template/dom-repeat.html

@@ -107,6 +107,7 @@
 
     is: 'dom-repeat',
     extends: 'template',
+    _template: null,
 
     /**
      * Fired whenever DOM is added or removed by this template (by

src/lib/template/dom-template.html

@@ -25,6 +25,7 @@
 
     is: 'dom-template',
     extends: 'template',
+    _template: null,
 
     behaviors: [
       Polymer.Templatizer

src/mini/template.html

@@ -25,8 +25,9 @@
 
     _prepTemplate: function() {
       // locate template using dom-module
-      this._template =
-        this._template || Polymer.DomModule.import(this.is, 'template');
+      if (this._template === undefined) {
+        this._template = Polymer.DomModule.import(this.is, 'template');  
+      }
       // stick finger in footgun
       if (this._template && this._template.hasAttribute('is')) {
         this._warn(this._logf('_prepTemplate', 'top-level Polymer template ' +

src/standard/styling.html

@@ -40,16 +40,20 @@
           this._encapsulateStyle = !nativeShadow &&
             Boolean(this._template);
         }
-        this._styles = this._collectStyles();
-        var cssText = styleTransformer.elementStyles(this);
-        if (cssText && this._template) {
-          var style = styleUtil.applyCss(cssText, this.is,
-            nativeShadow ? this._template.content : null);
-          // keep track of style when in document scope (polyfill) so we can
-          // attach property styles after it.
-          if (!nativeShadow) {
-            this._scopeStyle = style;
+        if (this._template) {
+          this._styles = this._collectStyles();
+          var cssText = styleTransformer.elementStyles(this);
+          if (cssText) {
+            var style = styleUtil.applyCss(cssText, this.is,
+              nativeShadow ? this._template.content : null);
+            // keep track of style when in document scope (polyfill) so we can
+            // attach property styles after it.
+            if (!nativeShadow) {
+              this._scopeStyle = style;
+            }
           }
+        } else {
+          this._styles = [];
         }
       },