Added unit tests for auto_scan_manager. Created switch access test target.

chrome/test/BUILD.gn

Index: chrome/test/BUILD.gn
diff --git a/chrome/test/BUILD.gn b/chrome/test/BUILD.gn
index 7f70680310606071a00cf412c1fa567fc576093d..85031a639eb11900928ce62d768e931d9ba59a81 100644
--- a/chrome/test/BUILD.gn
+++ b/chrome/test/BUILD.gn
@@ -3071,13 +3071,11 @@ js2gtest("unit_tests_js") {
     sources += [
       "../browser/resources/chromeos/braille_ime/braille_ime_unittest.gtestjs",
       "../browser/resources/chromeos/select_to_speak/select_to_speak_unittest.gtestjs",
-      "../browser/resources/chromeos/switch_access/tree_walker_unittest.gtestjs",
     ]
     extra_js_files += [
       "../browser/resources/chromeos/braille_ime/braille_ime.js",
       "../browser/resources/chromeos/select_to_speak/select_to_speak.js",
       "../browser/resources/chromeos/select_to_speak/test_support.js",
-      "../browser/resources/chromeos/switch_access/tree_walker.js",
     ]
   }
 }