Added auto-scan, made some small changes to how prefs are stored, refactored.

chrome/browser/resources/chromeos/switch_access/testable_tree_walker.js

Index: chrome/browser/resources/chromeos/switch_access/testable_tree_walker.js
diff --git a/chrome/browser/resources/chromeos/switch_access/testable_switch_access.js b/chrome/browser/resources/chromeos/switch_access/testable_tree_walker.js
similarity index 67%
rename from chrome/browser/resources/chromeos/switch_access/testable_switch_access.js
rename to chrome/browser/resources/chromeos/switch_access/testable_tree_walker.js
index c5cdde736627254bd5b0ed86d0aea4e907974889..bc12b274832842912427d44f11824f6a9f3e4b24 100644
--- a/chrome/browser/resources/chromeos/switch_access/testable_switch_access.js
+++ b/chrome/browser/resources/chromeos/switch_access/testable_tree_walker.js
@@ -3,16 +3,15 @@
 // found in the LICENSE file.
 
 /**
- * Subclass of SwitchAccess that exposes SwitchAccess's methods for testing.
+ * Subclass of AutomationTreeWalker that exposes AutomationTreeWalker's methods
+ * for testing.

[David Tseng, 2017/03/29 21:57:20]

@extends {AutomationTreeWalker}
(I know this doesn't get compiled).

[elichtenberg, 2017/03/30 21:46:56]

Done.

  */
-let TestableSwitchAccess = function() {
-  SwitchAccess.call(this);
+function TestableTreeWalker() {
+  AutomationTreeWalker.call(this);
 };
 
-TestableSwitchAccess.prototype = {
-  __proto__: SwitchAccess.prototype,
-
-  init_: function() {},
+TestableTreeWalker.prototype = {
+  __proto__: AutomationTreeWalker.prototype,
 
   getNextNode: function(node) {

[David Tseng, 2017/03/29 21:57:21]

I don't see that much value in having this in its own file since it has one
consumer. Up to you though. I would put it in the unit test file. Also, since
tests don't get compiled, you could access private members of the object.

[elichtenberg, 2017/03/30 21:46:56]

I agree. I'm just going to access the private members of AutomationTreeWalker,
and so I'm deleting this file.

     return this.getNextNode_(node);