Tweak isBrowserExtension()'s API

Tweak `isBrowserExtension()` to take just the `config.app` string that
it needs and not the entire `config` object as argument. This is
necessary for `isBrowserExtension()` to be called by `settings.js`
instead of `index.js` (as I want it to be in the future) - when it's
called by `settings.js` the `config` object as a whole won't be
available (and hasn't been constructed yet).

src/annotator/config/index.js

@@ -25,7 +25,7 @@ function configFrom(window_) {
     annotations: settings.annotations(window_.location.href),
   };
 
-  if (isBrowserExtension(config)) {
+  if (isBrowserExtension(config.app)) {
     return config;
   }
 

src/annotator/config/is-browser-extension.js

@@ -8,8 +8,8 @@
  *   website.
  *
  */
-function isBrowserExtension(config) {
-  return !(config.app.startsWith('http://') || config.app.startsWith('https://'));
+function isBrowserExtension(app) {
+  return !(app.startsWith('http://') || app.startsWith('https://'));
 }
 
 module.exports = isBrowserExtension;

src/annotator/config/test/is-browser-extension-test.js

@@ -31,7 +31,7 @@ describe('annotator.config.isBrowserExtension', function() {
     },
   ].forEach(function(test) {
     it('returns ' + test.returns + ' for ' + test.url, function() {
-      assert.equal(isBrowserExtension({app: test.url}), test.returns);
+      assert.equal(isBrowserExtension(test.url), test.returns);
     });
   });
 });