Print Preview: Merge NativeLayerStubs for tests

chrome/browser/resources/print_preview/native_layer.js

Index: chrome/browser/resources/print_preview/native_layer.js
diff --git a/chrome/browser/resources/print_preview/native_layer.js b/chrome/browser/resources/print_preview/native_layer.js
index 19a5231930c9556349d757bbbf3be6fe026c2422..3e513c979cd09eb1c05313ad424afdb92792b6a4 100644
--- a/chrome/browser/resources/print_preview/native_layer.js
+++ b/chrome/browser/resources/print_preview/native_layer.js
@@ -80,6 +80,27 @@ cr.define('print_preview', function() {
     this.eventTarget_ = new cr.EventTarget();
   }
 
+  /** @private {print_preview.NativeLayer} */

[dpapad, 2017/05/19 20:59:29]

?print_preview.NativeLayer

[rbpotter, 2017/05/20 00:43:59]

Done.

+  var currentInstance = null;
+
+  /**
+   * @return {!print_preview.NativeLayer} an instance of NativeLayer.

[dpapad, 2017/05/19 20:59:29]

Nit:
"an instance of NativeLayer." -> "The singleton instance."

[rbpotter, 2017/05/20 00:43:59]

Done.

+   * Creates a new NativeLayer if the current instance is not set.
+   */
+  NativeLayer.getInstance = function() {
+    if (currentInstance)

[dpapad, 2017/05/19 20:59:29]

This condition should be reversed I think. Also let's compare to null directly.

[rbpotter, 2017/05/20 00:43:59]

Done.

+      currentInstance = new NativeLayer();
+    return assert(currentInstance);
+  };
+
+  /**
+   * @param {!print_preview.NativeLayer} instance The NativeLayer instance
+   *     to set for print preview construction.
+   */
+  NativeLayer.setInstance = function(instance) {
+    currentInstance = instance;
+  };
+
   /**
    * Event types dispatched from the Chromium native layer.
    * @enum {string}