Print Preview: Use a computed property to set CrOS destination status

Slightly clean up the CrOS destination status code by using a computed
property to set |statusText_|. This allows the removal of the observer
on |destination| and manual calls of updateStatusText_(). Additionally,
remove the stale shouldShowStatus_() function.

Change-Id: I50011717b9643f137fdd67f12c580adcae289776
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2357070
Commit-Queue: Daniel Hosseinian <dhoss@chromium.org>
Reviewed-by: Rebekah Potter <rbpotter@chromium.org>
Cr-Commit-Position: refs/heads/master@{#799481}

chrome/browser/resources/print_preview/ui/destination_select_cros.js

@@ -41,11 +41,7 @@ Polymer({
     dark: Boolean,
 
     /** @type {!Destination} */
-    destination: {
-      type: Object,
-      observer: 'onDestinationChange_',
-    },
-
+    destination: Object,
 
     disabled: Boolean,
 
@@ -69,8 +65,12 @@ Polymer({
       value: PDF_DESTINATION_KEY,
     },
 
-    /** @private */
-    statusText_: String,
+    /** @private {string} */
+    statusText_: {
+      type: String,
+      computed:
+          'computeStatusText_(destination, destination.printerStatusReason)',
+    },
 
     /** @private {string} */
     backgroundImages_: {
@@ -294,10 +294,9 @@ Polymer({
 
     // If |printerStatus| is for the currently selected printer, use notifyPath
     // to trigger the destination printer status icon to recalculate its badge
-    // color. Next update the destination error status text.
+    // color and the destination error status text.
     if (this.destination && this.destination.key === destinationKey) {
       this.notifyPath(`destination.printerStatusReason`);
-      this.updateStatusText_();
     }
   },
 
@@ -339,47 +338,38 @@ Polymer({
                                PrinterStatusReason.UNKNOWN_REASON;
   },
 
-  /** @private */
-  onDestinationChange_: function() {
-    this.updateStatusText_();
-  },
-
   /**
-   * Check the current destination for an error status then set |statusText_|
-   * appropriately. If no error status exists, unset |statusText_|.
+   * @return {string}  An error status for the current destination. If no error
+   *     status exists, an empty string.
    * @private
    */
-  updateStatusText_: function() {
+  computeStatusText_: function() {
     // |destination| can be either undefined, or null here.
     if (!this.destination) {
-      this.statusText_ = '';
-      return;
+      return '';
     }
 
     // Cloudprint destinations contain their own status text.
     if (CloudOrigins.some(origin => origin === this.destination.origin)) {
-      this.statusText_ = this.destination.shouldShowInvalidCertificateError ?
+      return this.destination.shouldShowInvalidCertificateError ?
           this.i18n('noLongerSupportedFragment') :
           this.destination.connectionStatusText;
-      return;
     }
 
     // Only when the flag is enabled do we need to fetch a local printer status
     // error string.
     if (!this.printerStatusFlagEnabled_) {
-      this.statusText_ = '';
-      return;
+      return '';
     }
 
     const printerStatusReason = this.destination.printerStatusReason;
     if (!printerStatusReason ||
         printerStatusReason === PrinterStatusReason.NO_ERROR ||
         printerStatusReason === PrinterStatusReason.UNKNOWN_REASON) {
-      this.statusText_ = '';
-      return;
+      return '';
     }
 
-    this.statusText_ = this.getErrorString_(printerStatusReason);
+    return this.getErrorString_(printerStatusReason);
   },
 
   /**
@@ -392,14 +382,6 @@ Polymer({
     return errorStringKey ? this.i18n(errorStringKey) : '';
   },
 
-  /**
-   * @return {!boolean}
-   * @private
-   */
-  shouldShowStatus_: function() {
-    return !!this.statusText_;
-  },
-
   /**
    * True when the currently selected destination is a CrOS local printer.
    * @return {boolean}