Implementation of "Enable 2G" for Settings.

(1) Adds KEY_HIDE_ENABLE_2G_BOOL to CarrierConfigManager, and
(2) Adds new reason ALLOWED_NETWORK_TYPES_REASON_ENABLE_2G.

Test: manual & atest -c Enable2gPreferenceControllerTest
Bug: b/163168917
Change-Id: I81052549f8dde491697c35365320145fd24c3842
diff --git a/core/api/current.txt b/core/api/current.txt
index 1296dd19..ae9378e 100644
--- a/core/api/current.txt
+++ b/core/api/current.txt
@@ -40270,6 +40270,7 @@
     field public static final String KEY_GSM_ROAMING_NETWORKS_STRING_ARRAY = "gsm_roaming_networks_string_array";
     field public static final String KEY_HAS_IN_CALL_NOISE_SUPPRESSION_BOOL = "has_in_call_noise_suppression_bool";
     field public static final String KEY_HIDE_CARRIER_NETWORK_SETTINGS_BOOL = "hide_carrier_network_settings_bool";
+    field public static final String KEY_HIDE_ENABLE_2G = "hide_enable_2g_bool";
     field public static final String KEY_HIDE_ENHANCED_4G_LTE_BOOL = "hide_enhanced_4g_lte_bool";
     field public static final String KEY_HIDE_IMS_APN_BOOL = "hide_ims_apn_bool";
     field public static final String KEY_HIDE_LTE_PLUS_DATA_ICON_BOOL = "hide_lte_plus_data_icon_bool";
diff --git a/core/api/system-current.txt b/core/api/system-current.txt
index d7dc6ef..96ea49a 100644
--- a/core/api/system-current.txt
+++ b/core/api/system-current.txt
@@ -11944,6 +11944,7 @@
     field public static final String ACTION_SIM_CARD_STATE_CHANGED = "android.telephony.action.SIM_CARD_STATE_CHANGED";
     field public static final String ACTION_SIM_SLOT_STATUS_CHANGED = "android.telephony.action.SIM_SLOT_STATUS_CHANGED";
     field public static final int ALLOWED_NETWORK_TYPES_REASON_CARRIER = 2; // 0x2
+    field public static final int ALLOWED_NETWORK_TYPES_REASON_ENABLE_2G = 3; // 0x3
     field public static final int ALLOWED_NETWORK_TYPES_REASON_POWER = 1; // 0x1
     field public static final int ALLOWED_NETWORK_TYPES_REASON_USER = 0; // 0x0
     field public static final int CALL_WAITING_STATUS_DISABLED = 2; // 0x2
diff --git a/core/java/android/provider/Telephony.java b/core/java/android/provider/Telephony.java
index f013976e..7996f09 100644
--- a/core/java/android/provider/Telephony.java
+++ b/core/java/android/provider/Telephony.java
@@ -5286,7 +5286,8 @@
          * which network types are allowed for
          * {@link TelephonyManager#ALLOWED_NETWORK_TYPES_REASON_USER},
          * {@link TelephonyManager#ALLOWED_NETWORK_TYPES_REASON_POWER},
-         * {@link TelephonyManager#ALLOWED_NETWORK_TYPES_REASON_CARRIER}.
+         * {@link TelephonyManager#ALLOWED_NETWORK_TYPES_REASON_CARRIER},
+         * {@link TelephonyManager#ALLOWED_NETWORK_TYPES_REASON_ENABLE_2G}.
          * <P>Type: TEXT </P>
          *
          * @hide
diff --git a/core/java/android/telephony/PhoneStateListener.java b/core/java/android/telephony/PhoneStateListener.java
index 77f9c1a..e7ceada 100644
--- a/core/java/android/telephony/PhoneStateListener.java
+++ b/core/java/android/telephony/PhoneStateListener.java
@@ -1840,13 +1840,15 @@
          *
          * @param allowedNetworkTypesList Map associating all allowed network type reasons
          * ({@link TelephonyManager#ALLOWED_NETWORK_TYPES_REASON_USER},
-         * {@link TelephonyManager#ALLOWED_NETWORK_TYPES_REASON_POWER}, and
-         * {@link TelephonyManager#ALLOWED_NETWORK_TYPES_REASON_CARRIER}) with reason's allowed
+         * {@link TelephonyManager#ALLOWED_NETWORK_TYPES_REASON_POWER},
+         * {@link TelephonyManager#ALLOWED_NETWORK_TYPES_REASON_CARRIER}, and
+         * {@link TelephonyManager#ALLOWED_NETWORK_TYPES_REASON_ENABLE_2G}) with reason's allowed
          * network type values.
          * For example:
          * map{{TelephonyManager#ALLOWED_NETWORK_TYPES_REASON_USER, long type value},
          *     {TelephonyManager#ALLOWED_NETWORK_TYPES_REASON_POWER, long type value},
-         *     {TelephonyManager#ALLOWED_NETWORK_TYPES_REASON_CARRIER, long type value}}
+         *     {TelephonyManager#ALLOWED_NETWORK_TYPES_REASON_CARRIER, long type value},
+         *     {TelephonyManager#ALLOWED_NETWORK_TYPES_REASON_ENABLE_2G, long type value}}
          */
         @RequiresPermission(android.Manifest.permission.READ_PRIVILEGED_PHONE_STATE)
         void onAllowedNetworkTypesChanged(
diff --git a/telephony/java/android/telephony/CarrierConfigManager.java b/telephony/java/android/telephony/CarrierConfigManager.java
index 21cf3e5..dc6d7d5 100644
--- a/telephony/java/android/telephony/CarrierConfigManager.java
+++ b/telephony/java/android/telephony/CarrierConfigManager.java
@@ -4763,6 +4763,14 @@
     public static final String KEY_STORE_SIM_PIN_FOR_UNATTENDED_REBOOT_BOOL =
             "store_sim_pin_for_unattended_reboot_bool";
 
+     /**
+     * Determine whether "Enable 2G" toggle can be shown.
+     *
+     * Used to trade privacy/security against potentially reduced carrier coverage for some
+     * carriers.
+     */
+    public static final String KEY_HIDE_ENABLE_2G = "hide_enable_2g_bool";
+
     /** The default value for every variable. */
     private final static PersistableBundle sDefaults;
 
@@ -5320,6 +5328,7 @@
         sDefaults.putBoolean(KEY_NETWORK_TEMP_NOT_METERED_SUPPORTED_BOOL, true);
         sDefaults.putInt(KEY_DEFAULT_RTT_MODE_INT, 0);
         sDefaults.putBoolean(KEY_STORE_SIM_PIN_FOR_UNATTENDED_REBOOT_BOOL, true);
+        sDefaults.putBoolean(KEY_HIDE_ENABLE_2G, false);
     }
 
     /**
diff --git a/telephony/java/android/telephony/TelephonyManager.java b/telephony/java/android/telephony/TelephonyManager.java
index ee3a0ef..b1d8607a 100644
--- a/telephony/java/android/telephony/TelephonyManager.java
+++ b/telephony/java/android/telephony/TelephonyManager.java
@@ -8591,7 +8591,8 @@
     @IntDef({
             ALLOWED_NETWORK_TYPES_REASON_USER,
             ALLOWED_NETWORK_TYPES_REASON_POWER,
-            ALLOWED_NETWORK_TYPES_REASON_CARRIER
+            ALLOWED_NETWORK_TYPES_REASON_CARRIER,
+            ALLOWED_NETWORK_TYPES_REASON_ENABLE_2G
     })
     @Retention(RetentionPolicy.SOURCE)
     public @interface AllowedNetworkTypesReason {
@@ -8628,6 +8629,14 @@
     public static final int ALLOWED_NETWORK_TYPES_REASON_CARRIER = 2;
 
     /**
+     * To indicate allowed network type change is requested by the user via the 2G toggle.
+     *
+     * @hide
+     */
+    @SystemApi
+    public static final int ALLOWED_NETWORK_TYPES_REASON_ENABLE_2G = 3;
+
+    /**
      * Set the allowed network types of the device and
      * provide the reason triggering the allowed network change.
      * This can be called for following reasons
@@ -8636,6 +8645,8 @@
      * <li>Allowed network types control by power manager
      * {@link #ALLOWED_NETWORK_TYPES_REASON_POWER}
      * <li>Allowed network types control by carrier {@link #ALLOWED_NETWORK_TYPES_REASON_CARRIER}
+     * <li>Allowed network types control by the user-controlled "Allow 2G" toggle
+     * {@link #ALLOWED_NETWORK_TYPES_REASON_ENABLE_2G}
      * </ol>
      * This API will result in allowing an intersection of allowed network types for all reasons,
      * including the configuration done through other reasons.
@@ -8719,6 +8730,7 @@
             case TelephonyManager.ALLOWED_NETWORK_TYPES_REASON_USER:
             case TelephonyManager.ALLOWED_NETWORK_TYPES_REASON_POWER:
             case TelephonyManager.ALLOWED_NETWORK_TYPES_REASON_CARRIER:
+            case TelephonyManager.ALLOWED_NETWORK_TYPES_REASON_ENABLE_2G:
                 return true;
         }
         return false;