Increase initial number of files shown to 200

Also, set fileListIncrement from the same value as numFilesShown to
futureproof- don't want one to get modified without the other.

Bug: Issue 5877
Change-Id: Idbbb9a694d9c203489454299309fd4cec31a00bd

polygerrit-ui/app/elements/change/gr-file-list/gr-file-list_test.html

@@ -60,7 +60,7 @@ limitations under the License.
         reload: function() { return Promise.resolve(); },
       });
       element = fixture('basic');
-      element.numFilesShown = 75;
+      element.numFilesShown = 200;
       saveStub = sandbox.stub(element, '_saveReviewedState',
           function() { return Promise.resolve(); });
     });
@@ -69,6 +69,15 @@ limitations under the License.
       sandbox.restore();
     });
 
+    test('correct number of files are shown', function() {
+      element._files = _.times(500, function(i) {
+          return {__path: '/file' + i, lines_inserted: 9}; });
+      flushAsynchronousOperations();
+      assert.equal(
+          Polymer.dom(element.root).querySelectorAll('.file-row').length,
+          element.numFilesShown);
+    });
+
     test('get file list', function(done) {
       var getChangeFilesStub = sandbox.stub(element.$.restAPI, 'getChangeFiles',
           function() {