Allow users to opt in to native ShadowDOM even when a fully supported version is not available via ?shadow=native.

Author: sorvell

platform.js

@@ -16,8 +16,20 @@ function processFlags(flags) {
   } else {
     // truthy value for any of these flags, or failure to detect native
     // ShadowDOM, results in polyfill
-    flags.shadow = (flags.shadowdom || flags.shadow || flags.polyfill ||
-      !HTMLElement.prototype.createShadowRoot) && 'polyfill';
+    //flags.shadow = (flags.shadowdom || flags.shadow || flags.polyfill ||
+    // !HTMLElement.prototype.createShadowRoot) && 'polyfill';
+
+    // If any of these flags match 'native', then force native ShadowDOM; any
+    // other truthy value, or failure to detect native
+    // ShadowDOM, results in polyfill 
+    flags.shadow = (flags.shadow || flags.shadowdom || flags.polyfill);
+    if (flags.shadow === 'native') {
+      flags.shadow = false;
+    } else {
+      flags.shadow = flags.shadow || !HTMLElement.prototype.createShadowRoot
+          && 'polyfill';
+    }
+
 
     var ShadowDOMNative = [
       'src/patches-shadowdom-native.js'