Don't via via

Fixes #2371
Adds test.

h/static/scripts/directive/share-dialog.coffee

@@ -18,7 +18,11 @@ module.exports = ['crossframe', (crossframe) ->
     scope.$watchCollection (-> crossframe.frames), (frames) ->
       if not frames.length
         return
-      # XXX: Consider sharing multiple frames in the future?
+      # Check to see if we are on a via page. If so, we just return the URI.
+      re = /https:\/\/via\.hypothes\.is/
+      if re.test(frames[0].uri)
+        scope.viaPageLink = frames[0].uri
+      else
         scope.viaPageLink = 'https://via.hypothes.is/' + frames[0].uri
 
   restrict: 'A'

h/static/scripts/directive/test/share-dialog-test.coffee

@@ -30,3 +30,10 @@ describe 'share-dialog', ->
     $scope.$digest()
     assert.equal($scope.viaPageLink,
                  'https://via.hypothes.is/http://example.com')
+
+  it 'does not generate new via link if already on via', ->
+    $element = $compile('<div share-dialog="">')($scope)
+    fakeCrossFrame.frames.push({uri: ['https://via.hypothes.is/http://example.com']})
+    $scope.$digest()
+    assert.equal($scope.viaPageLink,
+                 'https://via.hypothes.is/http://example.com')