Adapt to deprecation of WindowCacheStats methods in JGit

Commit 42f0c7c9c ("Enhance WindowCache statistics") [1] deprecated
the getOpenFiles() and getOpenByteCount() methods.

Also adjust to the number of open files now being long instead
of integer.

[1] https://git.eclipse.org/r/#/c/153601/

Change-Id: I9f7ebb11ddf541a6601406d713f7e90065804e48

java/com/google/gerrit/metrics/proc/JGitMetricModule.java

@@ -28,12 +28,12 @@ public class JGitMetricModule extends MetricModule {
         new Description("Bytes of memory retained in JGit block cache.")
             .setGauge()
             .setUnit(Units.BYTES),
-        WindowCacheStats::getOpenBytes);
+        () -> WindowCacheStats.getStats().getOpenByteCount());
 
     metrics.newCallbackMetric(
         "jgit/block_cache/open_files",
-        Integer.class,
+        Long.class,
         new Description("File handles held open by JGit block cache.").setGauge().setUnit("fds"),
-        WindowCacheStats::getOpenFiles);
+        () -> WindowCacheStats.getStats().getOpenFileCount());
   }
 }

java/com/google/gerrit/server/restapi/config/GetSummary.java

@@ -126,8 +126,8 @@ public class GetSummary implements RestReadView<ConfigResource> {
     long mTotal = r.totalMemory();
     long mInuse = mTotal - mFree;
 
-    int jgitOpen = WindowCacheStats.getOpenFiles();
-    long jgitBytes = WindowCacheStats.getOpenBytes();
+    long jgitOpen = WindowCacheStats.getStats().getOpenFileCount();
+    long jgitBytes = WindowCacheStats.getStats().getOpenByteCount();
 
     MemSummaryInfo memSummaryInfo = new MemSummaryInfo();
     memSummaryInfo.total = bytes(mTotal);
@@ -135,7 +135,7 @@ public class GetSummary implements RestReadView<ConfigResource> {
     memSummaryInfo.free = bytes(mFree);
     memSummaryInfo.buffers = bytes(jgitBytes);
     memSummaryInfo.max = bytes(mMax);
-    memSummaryInfo.openFiles = toInteger(jgitOpen);
+    memSummaryInfo.openFiles = Long.valueOf(jgitOpen);
     return memSummaryInfo;
   }
 
@@ -258,7 +258,7 @@ public class GetSummary implements RestReadView<ConfigResource> {
     public String free;
     public String buffers;
     public String max;
-    public Integer openFiles;
+    public Long openFiles;
   }
 
   public static class ThreadSummaryInfo {

java/com/google/gerrit/sshd/commands/ShowCaches.java

@@ -297,6 +297,10 @@ final class ShowCaches extends SshCommand {
     return i != null ? i : 0;
   }
 
+  private static long nullToZero(Long i) {
+    return i != null ? i : 0;
+  }
+
   private void sshSummary() {
     IoAcceptor acceptor = daemon.getIoAcceptor();
     if (acceptor == null) {