Add knownCerts to system API and copy constructor.

PermissionInfo.PROTECTION_FLAG_KNOWN_SIGNER is already @SystemApi, and
we need system API for accessing the actual certs in the modularized
permission subsystem.

The copy constructor missed knownCerts in ag/13504004 and is fixed now.
knownCerts isn't deep copied in the copy constructor because
PackageItemInfo.metaData isn't deep copied either.

Bug: 182523293
Test: atest CtsContentTestCases:PermissionInfoTest
Change-Id: I784764fdf7238f6b10455ff40c693de0823a94cb

core/api/system-current.txt

@@ -3617,6 +3617,7 @@ package android.content.pm {
     field public static final int PROTECTION_FLAG_SYSTEM_TEXT_CLASSIFIER = 65536; // 0x10000
     field @Deprecated public static final int PROTECTION_FLAG_WELLBEING = 131072; // 0x20000
     field @Nullable public final String backgroundPermission;
+    field @NonNull public java.util.Set<java.lang.String> knownCerts;
     field @StringRes public int requestRes;
   }
 

core/java/android/content/pm/PermissionInfo.java

@@ -20,6 +20,7 @@ import android.annotation.IntDef;
 import android.annotation.NonNull;
 import android.annotation.Nullable;
 import android.annotation.StringRes;
+import android.annotation.SuppressLint;
 import android.annotation.SystemApi;
 import android.annotation.TestApi;
 import android.compat.annotation.UnsupportedAppUsage;
@@ -33,6 +34,7 @@ import com.android.internal.util.Parcelling.BuiltIn.ForStringSet;
 
 import java.lang.annotation.Retention;
 import java.lang.annotation.RetentionPolicy;
+import java.util.Collections;
 import java.util.Set;
 
 /**
@@ -486,7 +488,10 @@ public class PermissionInfo extends PackageItemInfo implements Parcelable {
      *
      * @hide
      */
-    public @Nullable Set<String> knownCerts;
+    // Already being used as mutable and most other fields in this class are also mutable.
+    @SuppressLint("MutableBareField")
+    @SystemApi
+    public @NonNull Set<String> knownCerts = Collections.emptySet();
 
     /** @hide */
     public static int fixProtectionLevel(int level) {
@@ -620,6 +625,8 @@ public class PermissionInfo extends PackageItemInfo implements Parcelable {
         descriptionRes = orig.descriptionRes;
         requestRes = orig.requestRes;
         nonLocalizedDescription = orig.nonLocalizedDescription;
+        // Note that knownCerts wasn't properly copied before Android U.
+        knownCerts = orig.knownCerts;
     }
 
     /**