[DevTools] Set minimum height of storage's key-value table

Set the minimum height of storage panel's key-value table so that the
preview panel down below won't obscure it when dragged upward, confusing
the users.
Screenshot: https://imgur.com/a/VhC4X7x

Bug: 865091
Change-Id: I152f9082f6dd1646a1e8eaeb4d9111b181546553
Reviewed-on: https://chromium-review.googlesource.com/1220477
Commit-Queue: Haihong Li (Harley) <hhli@chromium.org>
Reviewed-by: Erik Luo <luoe@chromium.org>
Cr-Commit-Position: refs/heads/master@{#590453}

third_party/blink/renderer/devtools/front_end/resources/DOMStorageItemsView.js

@@ -53,7 +53,9 @@ Resources.DOMStorageItemsView = class extends Resources.StorageItemsView {
 
     this._previewPanel = new UI.VBox();
     const resizer = this._previewPanel.element.createChild('div', 'preview-panel-resizer');
-    this._splitWidget.setMainWidget(this._dataGrid.asWidget());
+    const dataGridWidget = this._dataGrid.asWidget();
+    dataGridWidget.setMinimumSize(0, 50);
+    this._splitWidget.setMainWidget(dataGridWidget);
     this._splitWidget.setSidebarWidget(this._previewPanel);
     this._splitWidget.installResizer(resizer);