[Devtools] Cleanup DataGrid's typecast and identifier naming

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

Index: third_party/WebKit/Source/devtools/front_end/resources/ServiceWorkerCacheViews.js
diff --git a/third_party/WebKit/Source/devtools/front_end/resources/ServiceWorkerCacheViews.js b/third_party/WebKit/Source/devtools/front_end/resources/ServiceWorkerCacheViews.js
index db130b3a2f97049789077f8d42789e0e40da8d8e..90a0590be53c27a3f810f35535bdcce0e48dbee8 100644
--- a/third_party/WebKit/Source/devtools/front_end/resources/ServiceWorkerCacheViews.js
+++ b/third_party/WebKit/Source/devtools/front_end/resources/ServiceWorkerCacheViews.js
@@ -36,13 +36,12 @@ WebInspector.ServiceWorkerCacheView.prototype = {
      */
     _createDataGrid: function()
     {
-        var columns = [];
-        columns.push({id: "number", title: WebInspector.UIString("#"), width: "50px"});
-        columns.push({id: "request", title: WebInspector.UIString("Request")});
-        columns.push({id: "response", title: WebInspector.UIString("Response")});
-
-        var dataGrid = new WebInspector.DataGrid(columns, undefined, this._deleteButtonClicked.bind(this), this._updateData.bind(this, true));
-        return dataGrid;
+        var columns = /** @type {!Array<!WebInspector.DataGrid.ColumnDescriptor>} */ ([
+            {id: "number", title: WebInspector.UIString("#"), width: "50px"},
+            {id: "request", title: WebInspector.UIString("Request")},
+            {id: "response", title: WebInspector.UIString("Response")}
+        ]);
+        return new WebInspector.DataGrid(columns, undefined, this._deleteButtonClicked.bind(this), this._updateData.bind(this, true));
     },
 
     _createEditorToolbar: function()