Merge pull request #4291 from Polymer/2.0-dom-module-assetpath

set assetpath

Author: kevinpschaaf

src/elements/element.html

@@ -408,9 +408,8 @@
         var module = Polymer.DomModule.import(this.constructor.is);
         var root = '';
         if (module) {
-          var assetPath = module.getAttribute('assetpath') || '';
           root = Polymer.ResolveUrl.resolveUrl(
-            assetPath, module.ownerDocument.baseURI);
+            module.assetpath, module.ownerDocument.baseURI);
         }
         return Polymer.ResolveUrl.resolveUrl(url, root);
       }

src/legacy/dom-module.html

@@ -40,6 +40,25 @@
       }
     }
 
+    get assetpath() {
+      let assetpath = this.__assetpath || this.getAttribute('assetpath');
+      // Don't override existing assetpath.
+      if (assetpath) {}
+      // Polyfilled import.
+      else if (window.HTMLImports && !HTMLImports.useNative &&
+        HTMLImports.importForElement) {
+        const imp = HTMLImports.importForElement(this);
+        assetpath = imp ? imp.href : '';
+      }
+      // Native import.
+      else if (this.ownerDocument !== document && this.baseURI) {
+        assetpath = this.baseURI;
+      }
+      // Memoize.
+      this.__assetpath = assetpath;
+      return assetpath;
+    }
+
     /**
      * Registers the dom-module at a given id. This method should only be called
      * when a dom-module is imperatively created. For