Make polymer load warning throw and work more consistently. Helps add…

…ress https://github.com/Polymer/polymer-dev/issues/74.

build.json

@@ -10,10 +10,10 @@
   "build/end-if.js",
   "../URL/url.js",
   "src/lang.js",
-  "src/dom.js",
   "../HTMLImports/build.json",
   "../CustomElements/build.json",
   "src/patches-custom-elements.js",
+  "src/dom.js",
   "src/unresolved.js",
   "src/module.js"
 ]

platform.js

@@ -50,11 +50,10 @@ function processFlags(flags) {
       [
         '../URL/url.js',
         'src/lang.js',
-        'src/dom.js',
         '../HTMLImports/html-imports.js',
         '../CustomElements/custom-elements.js',
         'src/patches-custom-elements.js',
-
+        'src/dom.js',
         // these scripts are loaded in platform.js due to polyfill timing issues
         'src/unresolved.js',
         'src/module.js'

src/dom.js

@@ -75,17 +75,23 @@
     elementDeclarations = null;
   };
 
-  // Once DOMContent has loaded, any main document scripts that depend on
-  // Polymer() should have run. Calling Polymer() now is an error until
-  // polymer is imported.
-  window.addEventListener('DOMContentLoaded', function() {
+  function installPolymerWarning() {
     if (window.Polymer === polymerStub) {
       window.Polymer = function() {
-        console.error('You tried to use polymer without loading it first. To ' +
+        throw new Error('You tried to use polymer without loading it first. To ' +
           'load polymer, <link rel="import" href="' + 
           'components/polymer/polymer.html">');
       };
     }
-  });
+  }
+
+  // Once DOMContent has loaded, any main document scripts that depend on
+  // Polymer() should have run. Calling Polymer() now is an error until
+  // polymer is imported.
+  if (HTMLImports.useNative) {
+    installPolymerWarning();
+  } else {
+    addEventListener('DOMContentLoaded', installPolymerWarning);
+  }
 
 })(window.Platform);