Adapt to API change in dom-anchor-text-quote v4.x

Adapt to `toRange` returning null in 4.x rather than throwing an
exception if the quote is not found and add a test case for quote
anchoring failing.

See https://github.com/tilgovi/dom-anchor-text-quote/issues/10

h/static/scripts/annotator/anchoring/test/html-test.js

 'use strict';
 
 var html = require('../html');
-var unroll = require('../../../test/util').unroll;
 
+var toResult = require('../../../test/promise-util').toResult;
+var unroll = require('../../../test/util').unroll;
 var fixture = require('./html-anchoring-fixture.html');
 
 /** Return all text node children of `container`. */
@@ -190,6 +191,19 @@ describe('HTML anchoring', function () {
     return Promise.all(anchored);
   }, testCases);
 
+  describe('When anchoring fails', function () {
+    it('throws an error if anchoring using a quote fails', function () {
+      var quoteSelector = {
+        type: 'TextQuoteSelector',
+        exact: 'This text does not appear in the web page',
+      };
+
+      return toResult(html.anchor(container, [quoteSelector])).then(function (result) {
+        assert.equal(result.error.message, 'Quote not found');
+      });
+    });
+  });
+
   describe('Web page baselines', function () {
     var fixtures = require('./html-baselines');
     var frame;

h/static/scripts/annotator/anchoring/types.coffee

@@ -101,7 +101,10 @@ class TextQuoteAnchor
     }
 
   toRange: (options = {}) ->
-    domAnchorTextQuote.toRange(@root, this.toSelector(), options)
+    range = domAnchorTextQuote.toRange(@root, this.toSelector(), options)
+    if range == null
+      throw new Error('Quote not found')
+    range
 
 
 exports.RangeAnchor = RangeAnchor