Splitting interop support so `dart_support.js` is no longer required.

pkg/web_components/lib/interop_support.js

Index: pkg/web_components/lib/interop_support.js
diff --git a/runtime/bin/vmservice/observatory/deployed/web/packages/web_components/dart_support.js b/pkg/web_components/lib/interop_support.js
similarity index 61%
copy from runtime/bin/vmservice/observatory/deployed/web/packages/web_components/dart_support.js
copy to pkg/web_components/lib/interop_support.js
index 7ce882cef9a107d18d5fc8ec23de4d7df69673d8..790f8284bdbe5158035eb755bc2911eebca40770 100644
--- a/runtime/bin/vmservice/observatory/deployed/web/packages/web_components/dart_support.js
+++ b/pkg/web_components/lib/interop_support.js
@@ -2,74 +2,12 @@
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
-// Teaches dart2js about the wrapping that is done by the Shadow DOM polyfill.
-(function() {
-  var ShadowDOMPolyfill = window.ShadowDOMPolyfill;
-  if (!ShadowDOMPolyfill) return;
-
-  // TODO(sigmund): remove the userAgent check once 1.6 rolls as stable.
-  // See: dartbug.com/18463
-  if (navigator.dartEnabled || (navigator.userAgent.indexOf('(Dart)') !== -1)) {
-    console.error("ShadowDOMPolyfill polyfill was loaded in Dartium. This " +
-        "will not work. This indicates that Dartium's Chrome version is " +
-        "not compatible with this version of web_components.");
-  }
-
-  var needsConstructorFix = window.constructor === window.Window;
-
-  // TODO(jmesserly): we need to wrap document somehow (a dart:html hook?)
-
-  // dartNativeDispatchHooksTransformer is described on initHooks() in
-  // sdk/lib/_internal/lib/native_helper.dart.
-  if (typeof window.dartNativeDispatchHooksTransformer == 'undefined')
-    window.dartNativeDispatchHooksTransformer = [];
-
-  window.dartNativeDispatchHooksTransformer.push(function(hooks) {
-    var NodeList = ShadowDOMPolyfill.wrappers.NodeList;
-    var ShadowRoot = ShadowDOMPolyfill.wrappers.ShadowRoot;
-    var unwrapIfNeeded = ShadowDOMPolyfill.unwrapIfNeeded;
-    var originalGetTag = hooks.getTag;
-    hooks.getTag = function getTag(obj) {
-      // TODO(jmesserly): do we still need these?
-      if (obj instanceof NodeList) return 'NodeList';
-      if (obj instanceof ShadowRoot) return 'ShadowRoot';
-      if (MutationRecord && (obj instanceof MutationRecord))
-          return 'MutationRecord';
-      if (MutationObserver && (obj instanceof MutationObserver))
-          return 'MutationObserver';
-
-      // TODO(jmesserly): this prevents incorrect interaction between ShadowDOM
-      // and dart:html's <template> polyfill. Essentially, ShadowDOM is
-      // polyfilling native template, but our Dart polyfill fails to detect this
-      // because the unwrapped node is an HTMLUnknownElement, leading it to
-      // think the node has no content.
-      if (obj instanceof HTMLTemplateElement) return 'HTMLTemplateElement';
-
-      var unwrapped = unwrapIfNeeded(obj);
-      if (unwrapped && (needsConstructorFix || obj !== unwrapped)) {
-        // Fix up class names for Firefox, or if using the minified polyfill.
-        // dart2js prefers .constructor.name, but there are all kinds of cases
-        // where this will give the wrong answer.
-        var ctor = obj.constructor
-        if (ctor === unwrapped.constructor) {
-          var name = ctor._ShadowDOMPolyfill$cacheTag_;
-          if (!name) {
-            name = originalGetTag(unwrapped);
-            ctor._ShadowDOMPolyfill$cacheTag_ = name;
-          }
-          return name;
-        }
-
-        obj = unwrapped;
-      }
-      return originalGetTag(obj);
-    }
-  });
-})();
-
 // Updates document.registerElement so Dart can see when Javascript custom
 // elements are created, and wrap them to provide a Dart friendly API.
 (function (doc) {
+  if (window._dart_register_element_interop_support) return;
+  window._dart_register_element_interop_support = true;
+
   var upgraders = {};       // upgrader associated with a custom-tag.
   var unpatchableTags = {}; // set of custom-tags that can't be patched.
   var pendingElements = {}; // will upgrade when/if an upgrader is installed.
@@ -159,7 +97,7 @@
   // Native custom elements outside the app in Chrome have constructor
   // names like "x-tag", which need to be translated to the DOM
   // element they extend.  When using the shadow dom polyfill this is
-  // take care of above.
+  // taken care of in dart_support.js.
   var ShadowDOMPolyfill = window.ShadowDOMPolyfill;
   if (!ShadowDOMPolyfill) {
     // dartNativeDispatchHooksTransformer is described on initHooks() in
@@ -175,7 +113,7 @@
           var match = s.match(/^\[object ([A-Za-z]*Element)\]$/);
           if (match) {
             return match[1];
-	  }
+          }
           return originalGetUnknownTag(o, tag);
         }
       };