DevTools: Set a minimum height on the WebSocketFrameView

This prevents the user from accidentally hiding the frame view
completely and being unable to figure out how to get it back.

Bug: 895548
Change-Id: I39f503faa680bc136b14e6e521a1528ab594feff
Reviewed-on: https://chromium-review.googlesource.com/c/1281873Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Commit-Queue: Joel Einbinder <einbinder@chromium.org>
Cr-Commit-Position: refs/heads/master@{#600136}

third_party/blink/renderer/devtools/front_end/network/ResourceWebSocketFrameView.js

@@ -81,6 +81,7 @@ Network.ResourceWebSocketFrameView = class extends UI.VBox {
     const mainContainer = new UI.VBox();
     mainContainer.element.appendChild(this._mainToolbar.element);
     this._dataGrid.asWidget().show(mainContainer.element);
+    mainContainer.setMinimumSize(0, 72);
     this._splitWidget.setMainWidget(mainContainer);
 
     this._frameEmptyWidget = new UI.EmptyWidget(Common.UIString('Select frame to browse its content.'));