Fix backup and restore for default browser app.

This was broken by ag/6216880 back in Q because it didn't take into
account that writeDefaultAppsLPr() is also used by
getDefaultAppsBackup(), so that it didn't modify
getDefaultAppsBackup() to read the browser role instead when
effectively removing pm/Settings.mDefaultBrowserApp.

This CL fixes the regression in a minimal and backwards-compatible
way. It extracts the XML related code into a static method, and makes
getDefaultAppsBackup() use that static method by passing in the
current default browser obtained from the browser role.

Bug: 271337188
Test: manually perform a restore via cable and verify that the source
      device provided its current default browser to backup helper via
      locally added log.
Change-Id: I1fde685049e9f3371bbef6956418f9a7eb5ff850

services/core/java/com/android/server/pm/PackageManagerService.java

@@ -7408,6 +7408,11 @@ public class PackageManagerService implements PackageSender, TestUtilityService
                 callback);
     }
 
+    @Nullable
+    String getDefaultBrowser(@UserIdInt int userId) {
+        return mDefaultAppProvider.getDefaultBrowser(userId);
+    }
+
     void setDefaultBrowser(@Nullable String packageName, boolean async, @UserIdInt int userId) {
         mDefaultAppProvider.setDefaultBrowser(packageName, async, userId);
     }

services/core/java/com/android/server/pm/PreferredActivityHelper.java

@@ -557,9 +557,8 @@ final class PreferredActivityHelper {
             serializer.startDocument(null, true);
             serializer.startTag(null, TAG_DEFAULT_APPS);
 
-            synchronized (mPm.mLock) {
+            final String defaultBrowser = mPm.getDefaultBrowser(userId);
-                mPm.mSettings.writeDefaultAppsLPr(serializer, userId);
+            Settings.writeDefaultApps(serializer, defaultBrowser);
-            }
 
             serializer.endTag(null, TAG_DEFAULT_APPS);
             serializer.endDocument();
@@ -584,12 +583,7 @@ final class PreferredActivityHelper {
             parser.setInput(new ByteArrayInputStream(backup), StandardCharsets.UTF_8.name());
             restoreFromXml(parser, userId, TAG_DEFAULT_APPS,
                     (parser1, userId1) -> {
-                        final String defaultBrowser;
+                        final String defaultBrowser = Settings.readDefaultApps(parser1);
-                        synchronized (mPm.mLock) {
-                            mPm.mSettings.readDefaultAppsLPw(parser1, userId1);
-                            defaultBrowser = mPm.mSettings.removeDefaultBrowserPackageNameLPw(
-                                    userId1);
-                        }
                         if (defaultBrowser != null) {
                             mPm.setDefaultBrowser(defaultBrowser, false, userId1);
                         }

services/core/java/com/android/server/pm/Settings.java

@@ -1691,6 +1691,19 @@ public final class Settings implements Watchable, Snappable, ResilientAtomicFile
 
     void readDefaultAppsLPw(XmlPullParser parser, int userId)
             throws XmlPullParserException, IOException {
+        String defaultBrowser = readDefaultApps(parser);
+        if (defaultBrowser != null) {
+            mDefaultBrowserApp.put(userId, defaultBrowser);
+        }
+    }
+
+    /**
+     * @return the package name for the default browser app, or {@code null} if none.
+     */
+    @Nullable
+    static String readDefaultApps(@NonNull XmlPullParser parser)
+            throws XmlPullParserException, IOException {
+        String defaultBrowser = null;
         int outerDepth = parser.getDepth();
         int type;
         while ((type = parser.next()) != XmlPullParser.END_DOCUMENT
@@ -1700,8 +1713,7 @@ public final class Settings implements Watchable, Snappable, ResilientAtomicFile
             }
             String tagName = parser.getName();
             if (tagName.equals(TAG_DEFAULT_BROWSER)) {
-                String packageName = parser.getAttributeValue(null, ATTR_PACKAGE_NAME);
+                defaultBrowser = parser.getAttributeValue(null, ATTR_PACKAGE_NAME);
-                mDefaultBrowserApp.put(userId, packageName);
             } else if (tagName.equals(TAG_DEFAULT_DIALER)) {
                 // Ignored.
             } else {
@@ -1711,6 +1723,7 @@ public final class Settings implements Watchable, Snappable, ResilientAtomicFile
                 XmlUtils.skipCurrentTag(parser);
             }
         }
+        return defaultBrowser;
     }
 
     void readBlockUninstallPackagesLPw(TypedXmlPullParser parser, int userId)
@@ -2085,8 +2098,13 @@ public final class Settings implements Watchable, Snappable, ResilientAtomicFile
 
     void writeDefaultAppsLPr(XmlSerializer serializer, int userId)
             throws IllegalArgumentException, IllegalStateException, IOException {
-        serializer.startTag(null, TAG_DEFAULT_APPS);
         String defaultBrowser = mDefaultBrowserApp.get(userId);
+        writeDefaultApps(serializer, defaultBrowser);
+    }
+
+    static void writeDefaultApps(@NonNull XmlSerializer serializer, @Nullable String defaultBrowser)
+            throws IllegalArgumentException, IllegalStateException, IOException {
+        serializer.startTag(null, TAG_DEFAULT_APPS);
         if (!TextUtils.isEmpty(defaultBrowser)) {
             serializer.startTag(null, TAG_DEFAULT_BROWSER);
             serializer.attribute(null, ATTR_PACKAGE_NAME, defaultBrowser);