Focus and tab between diff preferences inputs

Previously, the diff preferences form did not automatically focus to the
first textfield and did not allow tabbing between input fields. This
change adds autofocus when the overlay is opened and allows for tabbing
between the other input fields in the modal.

Bug: Issue 4140
Change-Id: If15812bb4404ca4061597755eeaf68d4cae23b3f

polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.html

diff --git a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.html b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.html
index 979ed55..14fd2b7 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.html
+++ b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view_test.html
@@ -36,7 +36,7 @@
   <template>
     <div></div>
   </template>
-</text-fixture>
+</test-fixture>
 
 <script>
   suite('gr-diff-view tests', function() {
@@ -103,7 +103,9 @@
           'Should navigate to /c/42/');
       assert.equal(element.changeViewState.selectedFileIndex, 0);
 
-      var showPrefsStub = sinon.stub(element.$.prefsOverlay, 'open');
+      var showPrefsStub = sinon.stub(element.$.prefsOverlay, 'open',
+          function() { return Promise.resolve({}); });
+
       MockInteractions.pressAndReleaseKeyOn(element, 188);  // ','
       assert(showPrefsStub.calledOnce);
 
@@ -131,6 +133,26 @@
       showStub.restore();
     });
 
+    test('saving diff preferences', function() {
+      var savePrefs = sinon.stub(element, '_handlePrefsSave');
+      var cancelPrefs = sinon.stub(element, '_handlePrefsCancel');
+      element.$.diffPreferences._handleSave();
+      assert(savePrefs.calledOnce);
+      assert(cancelPrefs.notCalled);
+      savePrefs.restore();
+      cancelPrefs.restore();
+    });
+
+    test('cancelling diff preferences', function() {
+      var savePrefs = sinon.stub(element, '_handlePrefsSave');
+      var cancelPrefs = sinon.stub(element, '_handlePrefsCancel');
+      element.$.diffPreferences._handleCancel();
+      assert(cancelPrefs.calledOnce);
+      assert(savePrefs.notCalled);
+      savePrefs.restore();
+      cancelPrefs.restore();
+    });
+
     test('keyboard shortcuts with patch range', function() {
       element._changeNum = '42';
       element._patchRange = {