Diagnostics: Wait for system info before showing app

- This change is needed to keep the order of the cards consistent since
  the battery status card is initially hidden.

Bug: 1125150
Test: browser_tests --gtest_filter=DiagnosticsApp*
Change-Id: Iaec2a4d37a11b083eb245f989ad9c937fb185c23
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2612152Reviewed-by: Zentaro Kavanagh <zentaro@chromium.org>
Commit-Queue: Michael Checo <michaelcheco@google.com>
Cr-Commit-Position: refs/heads/master@{#842573}

chromeos/components/diagnostics_ui/resources/diagnostics_app.html

@@ -43,7 +43,7 @@
     padding: 5px;
   }
 </style>
-<div id="diagnosticsContainer">
+<div id="diagnosticsContainer" hidden="[[!systemInfoReceived_]]">
   <div id="header">[[i18n('diagnosticsTitle')]]</div>
   <div class="overview-container">
     <overview-card id="overviewCard"></overview-card>

chromeos/components/diagnostics_ui/resources/diagnostics_app.js

@@ -46,6 +46,12 @@ Polymer({
       type: Boolean,
       value: false,
     },
+
+    /** @type {boolean} */
+    systemInfoReceived_: {
+      type: Boolean,
+      value: false,
+    },
   },
 
   /** @override */
@@ -66,6 +72,7 @@ Polymer({
    * @private
    */
   onSystemInfoReceived_(systemInfo) {
+    this.systemInfoReceived_ = true;
     this.showBatteryStatusCard_ = systemInfo.deviceCapabilities.hasBattery;
   },