Add policy management for on-screen keyboard.

chrome/test/data/policy/policy_test_cases.json

 {
   "-- Template --": {
     "intro": "Top-level entries map a policy name to its test parameters, described below.",
 
     "os": ["List of operating systems that support this policy. Valid values:", "win", "linux", "mac", "chromeos", "Defaults to empty if not specified."],
     "official_only": "Whether this policy exists in official builds only. Defaults to |false| if not specified.",
     "can_be_recommended": "Whether a recommended value may be set for the policy. Defaults to |false| if not specified.",
     "test_policy": "A policy dictionary that should make the preferences affected by this policy become policy-controlled. Usually just sets the current policy. Defaults to an empty dictionary if not specified.",
     "note": "If the policy affects any preferences, the following array should be specified with one entry per such preference.",
     "pref_mappings": [
@@ skipping 1904 matching lines @@
     "pref_mappings": [
       { "pref": "settings.a11y.screen_magnifier",
         "indicator_tests": [
           { "policy": { "ScreenMagnifierType": 1 } }
         ]
       },
       { "pref": "settings.a11y.screen_magnifier_type2" }
     ]
   },
 
+  "VirtualKeyboardEnabled": {
+    "os": ["chromeos"],
+    "test_policy": { "VirtualKeyboardEnabled": true },
+    "pref_mappings": [
+      { "pref": "settings.a11y.virtual_keyboard",
+        "indicator_tests": [
+          { "policy": { "VirtualKeyboardEnabled": true } }
+        ]
+      }
+    ]
+  },
+
   "AttestationEnabledForUser": {
     "os": ["chromeos"],
     "test_policy": { "AttestationEnabledForUser": true },
     "pref_mappings": [
       { "pref": "attestation.enabled" }
     ]
   },
 
   "AttestationExtensionWhitelist": {
     "os": ["chromeos"],
@@ skipping 202 matching lines @@
 
   "DeviceLoginScreenDefaultSpokenFeedbackEnabled" : {
   },
 
   "DeviceLoginScreenDefaultHighContrastEnabled" : {
   },
 
   "DeviceLoginScreenDefaultScreenMagnifierType" : {
   },
 
+  "DeviceLoginScreenDefaultVirtualKeyboardEnabled" : {
+  },
+
   "UptimeLimit": {
   },
 
   "RebootAfterUpdate": {
   },
 
   "AttestationEnabledForDevice": {
   },
 
   "AttestationForContentProtectionEnabled": {
@@ skipping 27 matching lines @@
 
   "AdditionalLaunchParameters": {
   },
 
   "SuppressChromeFrameTurndownPrompt": {
   },
 
   "SkipMetadataCheck": {
   }
 }