Pass ShowAccessibilityOptionsInSystemTrayMenu policy to the a11y team

As an effort to offload the policy team. Check details in the
https://crbug.com/1213081

Also added test cases for the policy

Bug: 1213081, 1213429, b:240372457
Change-Id: I1a813fb923372a6ea27591c9470ac41df18ee226
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3804569
Commit-Queue: Roman Sorokin <rsorokin@chromium.org>
Auto-Submit: Roman Sorokin <rsorokin@chromium.org>
Reviewed-by: Josiah Krutz <josiahk@google.com>
Commit-Queue: Josiah Krutz <josiahk@google.com>
Cr-Commit-Position: refs/heads/main@{#1030613}

chrome/test/data/policy/policy_test_cases.json

@@ -9333,12 +9333,32 @@
       "chromeos_ash"
     ],
     "policy_pref_mapping_tests": [
+      {
+        "note": "Default value (no policies set).",
+        "prefs": {
+          "settings.a11y.enable_menu": {
+            "default_value": false
+          }
+        }
+      },
       {
         "policies": {
           "ShowAccessibilityOptionsInSystemTrayMenu": true
         },
         "prefs": {
-          "settings.a11y.enable_menu": {}
+          "settings.a11y.enable_menu": {
+            "value": true
+          }
+        }
+      },
+      {
+        "policies": {
+          "ShowAccessibilityOptionsInSystemTrayMenu": false
+        },
+        "prefs": {
+          "settings.a11y.enable_menu": {
+            "value": false
+          }
         }
       }
     ]

components/policy/resources/policy_templates.json

@@ -14968,7 +14968,7 @@
     },
     {
       'name': 'ShowAccessibilityOptionsInSystemTrayMenu',
-      'owners': ['file://components/policy/resources/OWNERS', 'rsorokin@chromium.org'],
+      'owners': ['josiahk@google.com', 'file://ui/accessibility/OWNERS'],
       'type': 'main',
       'schema': { 'type': 'boolean' },
       'supported_on': ['chrome_os:27-'],