Revert to Default Settings

Add functionality to the revert default settings button. This currently
writes a null value to the ENABLE_TARE constant. In the future this will
also make the AlarmManager and JobScheduler constants null so that the
default values are used instead of custom config values.

Bug: 195543827

Test: Click on revert to default settings button, check that the value
for ENABLE_TARE is null by running "adb shell settings get global
enable_tare" in the command line

Change-Id: I558e8f1121021eca3224e4bc9b26bbe0dd2467c7

src/com/android/settings/development/tare/TareHomePage.java

@@ -23,6 +23,7 @@ import static com.android.settings.development.tare.DropdownActivity.POLICY_JOB_
 import android.app.Activity;
 import android.content.Intent;
 import android.os.Bundle;
+import android.provider.Settings;
 import android.view.View;
 import android.widget.Button;
 import android.widget.CompoundButton;
@@ -66,6 +67,8 @@ public class TareHomePage extends Activity {
     // TODO: Establish default TARE values and make this method revert all settings back to default.
     public void revertSettings(View v) {
         Toast.makeText(this, R.string.tare_settings_reverted_toast, Toast.LENGTH_LONG).show();
+        Settings.Global.putString(getApplicationContext().getContentResolver(),
+                Settings.Global.ENABLE_TARE, null);
     }
 
     /** Opens up the AlarmManager TARE policy page with its factors to view and edit */