[DevTools] Avoid exception when calling setStriped

SortableDataGrid.create may return null in some cases, subsequent call
to setStriped in such cases results in an exception logged.

Change-Id: I3f125c5747aeeaf54fce6596bd8451e2eb61b124
Reviewed-on: https://chromium-review.googlesource.com/518505Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Reviewed-by: Andrey Kosyakov <caseq@chromium.org>
Commit-Queue: Eugene Ostroukhov <eostroukhov@chromium.org>
Cr-Commit-Position: refs/heads/master@{#475777}

third_party/WebKit/Source/devtools/front_end/resources/DatabaseQueryView.js

@@ -135,10 +135,10 @@ Resources.DatabaseQueryView = class extends UI.VBox {
 
   _queryFinished(query, columnNames, values) {
     var dataGrid = DataGrid.SortableDataGrid.create(columnNames, values);
-    dataGrid.setStriped(true);
     var trimmedQuery = query.trim();
 
     if (dataGrid) {
+      dataGrid.setStriped(true);
       dataGrid.renderInline();
       this._appendViewQueryResult(trimmedQuery, dataGrid.asWidget());
       dataGrid.autoSizeColumns(5);

third_party/WebKit/Source/devtools/front_end/resources/DatabaseTableView.js

@@ -77,13 +77,13 @@ Resources.DatabaseTableView = class extends UI.SimpleView {
     this.element.removeChildren();
 
     this._dataGrid = DataGrid.SortableDataGrid.create(columnNames, values);
-    this._dataGrid.setStriped(true);
     this._visibleColumnsInput.setVisible(!!this._dataGrid);
     if (!this._dataGrid) {
       this._emptyWidget = new UI.EmptyWidget(Common.UIString('The “%s”\ntable is empty.', this.tableName));
       this._emptyWidget.show(this.element);
       return;
     }
+    this._dataGrid.setStriped(true);
     this._dataGrid.asWidget().show(this.element);
     this._dataGrid.autoSizeColumns(5);