Internet detail dialog: Focus the action button on load.

This is modeled after the same functionality in the internet detail
page implementation.

R=stevenjb@chromium.org

Bug: 999474
Test: none
Change-Id: If5dcac633d5881aa04878b0e57223a437c9af4bb
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1793808
Commit-Queue: James Hawkins <jhawkins@chromium.org>
Reviewed-by: Steven Bennetts <stevenjb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#695049}

chrome/browser/resources/chromeos/internet_detail_dialog/internet_detail_dialog.html

@@ -76,7 +76,7 @@
     </style>
 
     <!-- Title section: Icon + name + connection state. -->
-    <div class="section first">
+    <div id="title" class="section first">
       <div class="start layout horizontal center">
         <cr-network-icon
             show-technology-badge="[[showTechnologyBadge_]]"

chrome/browser/resources/chromeos/internet_detail_dialog/internet_detail_dialog.js

@@ -24,7 +24,10 @@ Polymer({
     guid: String,
 
     /** @private {!chromeos.networkConfig.mojom.ManagedProperties|undefined} */
-    managedProperties_: Object,
+    managedProperties_: {
+      type: Object,
+      observer: 'managedPropertiesChanged_',
+    },
 
     /** @private {?OncMojo.DeviceStateProperties} */
     deviceState_: {
@@ -54,6 +57,12 @@ Polymer({
     },
   },
 
+  /**
+   * Set to true once the action button has been focused.
+   * @private {boolean}
+   */
+  didSetFocus_: false,
+
   /**
    * Set to true to once the initial properties have been received. This
    * prevents setProperties from being called when setting default properties.
@@ -134,6 +143,21 @@ Polymer({
     };
   },
 
+  /** @private */
+  managedPropertiesChanged_: function() {
+    assert(this.managedProperties_);
+
+    // Focus the action button once the initial state is set.
+    if (!this.didSetFocus_ &&
+        this.showConnectDisconnect_(this.managedProperties_)) {
+      const button = this.$$('#title .action-button:not([hidden])');
+      if (button) {
+        button.focus();
+        this.didSetFocus_ = true;
+      }
+    }
+  },
+
   /** @private */
   close_: function() {
     chrome.send('dialogClose');