Switch back to acorn for JS tokenization

package.json

@@ -13,6 +13,7 @@
     "polymer-bundler": "lib/bin/polymer-bundler.js"
   },
   "dependencies": {
+    "acorn": "4.0.4",
     "clone": "^2.1.0",
     "command-line-args": "^3.0.1",
     "command-line-usage": "^3.0.3",
@@ -27,6 +28,7 @@
     "source-map": "^0.5.6"
   },
   "devDependencies": {
+    "@types/acorn": "^4.0.1",
     "@types/chai": "^3.4.30",
     "@types/clone": "^0.1.30",
     "@types/mocha": "^2.2.29",

src/source-map.ts

@@ -12,8 +12,8 @@
  * http://polymer.github.io/PATENTS.txt
  */
 
+import * as acorn from 'acorn';
 import * as dom5 from 'dom5';
-import * as espree from 'espree';
 import * as parse5 from 'parse5';
 import {Analyzer} from 'polymer-analyzer';
 import {AnalysisContext} from 'polymer-analyzer/lib/core/analysis-context';
@@ -50,9 +50,9 @@ function createJsIdentitySourcemap(
     lineOffset: number,
     firstLineCharOffset: number) {
   const generator = new SourceMapGenerator();
-  const tokens =
-      espree.tokenize(sourceContent, {loc: true} as espree.ParseOpts);
-  tokens.forEach(token => {
+  const tokenizer = acorn.tokenizer(sourceContent, {locations: true});
+  for (let token = tokenizer.getToken(); token.type.label !== 'eof';
+       token = tokenizer.getToken()) {
     if (!token.loc) {
       return null;
     }
@@ -66,12 +66,12 @@ function createJsIdentitySourcemap(
       source: sourceUrl
     };
 
-    if (token.type === 'Identifier') {
+    if (token.type.label === 'name') {
       mapping.name = token.value;
     }
 
     generator.addMapping(mapping);
-  });
+  }
 
   return generator.toJSON();
 }