Add download attribute to diff view download link

Bug: Issue 7168
Change-Id: I0786720e54d166856a0ece05fdc9f15a4b9de19f
diff --git a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.html b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.html
index 440f44b..b5da3a0 100644
--- a/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.html
+++ b/polygerrit-ui/app/elements/diff/gr-diff-view/gr-diff-view.html
@@ -280,7 +280,9 @@
           </gr-patch-range-select>
           <span class="download desktop">
             <span class="separator">/</span>
-            <a class="downloadLink"
+            <a
+              class="downloadLink"
+              download
               href$="[[_computeDownloadLink(_changeNum, _patchRange, _path)]]">
               Download
             </a>
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 e239bf0..73dd94a 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
@@ -455,8 +455,10 @@
       element._fileList = ['chell.go', 'glados.txt', 'wheatley.md'];
       element._path = 'glados.txt';
       flushAsynchronousOperations();
-      assert.equal(element.$$('.downloadLink').getAttribute('href'),
+      const link = element.$$('.downloadLink');
+      assert.equal(link.getAttribute('href'),
           '/changes/42/revisions/10/patch?zip&path=glados.txt');
+      assert.isTrue(link.hasAttribute('download'));
     });
 
     test('file review status', done => {