[MS82.2] Add a rewriteSingle method that takes two timestamps

This CL provides a public method in FileRotator to
allow caller to write data to a specified standalone file.

This CL also fix a file name generatign error in platform
tools.

Test: NetworkStatsServiceTest NetworkStatsCollectionTest
Bug: 230289468
Change-Id: I17558f349cb2a33062972fe1af96a19356798692
Merged-In: I17558f349cb2a33062972fe1af96a19356798692
  (pure cherry-picked from ag/18408306)

core/java/android/net/netstats/NetworkStatsDataMigrationUtils.java

@@ -161,7 +161,7 @@ public class NetworkStatsDataMigrationUtils {
     @NonNull
     private static ArrayList<File> getPlatformFileListForPrefix(@NonNull @Prefix String prefix) {
         final ArrayList<File> list = new ArrayList<>();
-        final File platformFiles = new File(getPlatformBaseDir(), "netstats");
+        final File platformFiles = getPlatformBaseDir();
         if (platformFiles.exists()) {
             for (String name : platformFiles.list()) {
                 // Skip when prefix doesn't match.

core/java/com/android/internal/util/FileRotator.java

@@ -16,6 +16,7 @@
 
 package com.android.internal.util;
 
+import android.annotation.NonNull;
 import android.os.FileUtils;
 import android.util.Log;
 
@@ -281,6 +282,20 @@ public class FileRotator {
         }
     }
 
+    /**
+     * Process a single file atomically, with the given start and end timestamps.
+     * If a file with these exact start and end timestamps does not exist, a new
+     * empty file will be written.
+     */
+    public void rewriteSingle(@NonNull Rewriter rewriter, long startTimeMillis, long endTimeMillis)
+            throws IOException {
+        final FileInfo info = new FileInfo(mPrefix);
+
+        info.startMillis = startTimeMillis;
+        info.endMillis = endTimeMillis;
+        rewriteSingle(rewriter, info.build());
+    }
+
     /**
      * Read any rotated data that overlap the requested time range.
      */