Fixes https://github.com/Polymer/HTMLImports/issues/77.

src/Parser.js

@@ -217,10 +217,14 @@ var importParser = {
   },
   // determine the next element in the tree which should be parsed
   nextToParse: function() {
+    this._mayParse = [];
     return !this.parsingElement && this.nextToParseInDoc(mainDoc);
   },
   nextToParseInDoc: function(doc, link) {
-    if (doc) {
+    // use `marParse` list to avoid looping into the same document again
+    // since it could cause an iloop.
+    if (doc && this._mayParse.indexOf(doc) < 0) {
+      this._mayParse.push(doc);
       var nodes = doc.querySelectorAll(this.parseSelectorsForNode(doc));
       for (var i=0, l=nodes.length, p=0, n; (i<l) && (n=nodes[i]); i++) {
         if (!this.isParsed(n)) {

test/html/imports/load-a.html

@@ -0,0 +1,14 @@
+<!--
+    @license
+    Copyright (c) 2014 The Polymer Project Authors. All rights reserved.
+    This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
+    The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
+    The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
+    Code distributed by Google as part of the polymer project is also
+    subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
+-->
+<script>
+	loaded = window.loaded || [];
+	loaded.push('a');
+</script>
+<link rel="import" href="load-b.html">

test/html/imports/load-b.html

@@ -0,0 +1,15 @@
+<!--
+    @license
+    Copyright (c) 2014 The Polymer Project Authors. All rights reserved.
+    This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
+    The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
+    The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
+    Code distributed by Google as part of the polymer project is also
+    subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
+-->
+<script>
+	loaded = window.loaded || [];
+	loaded.push('b');
+</script>
+<link rel="import" href="load-a.html">
+<link rel="import" href="load-c.html">

test/html/imports/load-c.html

@@ -0,0 +1,15 @@
+<!--
+    @license
+    Copyright (c) 2014 The Polymer Project Authors. All rights reserved.
+    This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
+    The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
+    The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
+    Code distributed by Google as part of the polymer project is also
+    subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
+-->
+<script>
+	loaded = window.loaded || [];
+	loaded.push('c');
+</script>
+<link rel="import" href="load-d.html">
+<link rel="import" href="load-a.html">

test/html/imports/load-d.html

@@ -0,0 +1,14 @@
+<!--
+    @license
+    Copyright (c) 2014 The Polymer Project Authors. All rights reserved.
+    This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
+    The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
+    The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
+    Code distributed by Google as part of the polymer project is also
+    subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
+-->
+<script>
+  loaded = window.loaded || [];
+	loaded.push('d');
+</script>
+<link rel="import" href="load-b.html">

test/html/load-loop.html

@@ -0,0 +1,27 @@
+<!--
+    @license
+    Copyright (c) 2014 The Polymer Project Authors. All rights reserved.
+    This code may only be used under the BSD style license found at http://polymer.github.io/LICENSE.txt
+    The complete set of authors may be found at http://polymer.github.io/AUTHORS.txt
+    The complete set of contributors may be found at http://polymer.github.io/CONTRIBUTORS.txt
+    Code distributed by Google as part of the polymer project is also
+    subject to an additional IP rights grant found at http://polymer.github.io/PATENTS.txt
+-->
+<!doctype html>
+<html>
+  <head>
+    <title>load loop Test</title>
+    <script src="../../../tools/test/htmltest.js"></script>
+    <script src="../../../tools/test/chai/chai.js"></script>
+    <script src="../../html-imports.js"></script>
+    <link rel="import" href="imports/load-a.html">
+  </head>
+  <body>
+    <script>
+      document.addEventListener('HTMLImportsLoaded', function() {
+        chai.assert.deepEqual(loaded, ['a', 'b', 'c', 'd']);
+        done();
+      });
+    </script>
+  </body>
+</html>

test/js/tests.js

@@ -11,6 +11,7 @@ htmlSuite('HTMLImports', function() {
   htmlTest('html/style-paths.html');
   htmlTest('html/load.html');
   htmlTest('html/load-404.html');
+  htmlTest('html/load-loop.html');
   htmlTest('html/base/load-base.html');
   htmlTest('html/currentScript.html');
   htmlTest('html/dedupe.html');