Expose the reverse index size in the DfsPackDescription

This is analogous to the getPackSize() and getIndexSize() methods.

Change-Id: I207c0c93f9145826d84b3610eb4319fca074ee0d

org.eclipse.jgit/src/org/eclipse/jgit/storage/dfs/DfsPackDescription.java

@@ -164,6 +164,13 @@ public class DfsPackDescription implements Comparable<DfsPackDescription> {
 		return this;
 	}
 
+	/**
+	 * @return size of the reverse index, in bytes.
+	 */
+	public int getReverseIndexSize() {
+		return (int) Math.min(objectCount * 8, Integer.MAX_VALUE);
+	}
+
 	/** @return number of objects in the pack. */
 	public long getObjectCount() {
 		return objectCount;

org.eclipse.jgit/src/org/eclipse/jgit/storage/dfs/DfsPackFile.java

@@ -265,11 +265,9 @@ public final class DfsPackFile {
 					return revidx;
 			}
 
-			PackIndex fwdidx = idx(ctx);
-			PackReverseIndex revidx = new PackReverseIndex(fwdidx);
-			long objCnt = fwdidx.getObjectCount();
-			int sz = (int) Math.min(objCnt * 8, Integer.MAX_VALUE);
-			reverseIndex = cache.put(key, POS_REVERSE_INDEX, sz, revidx);
+			PackReverseIndex revidx = new PackReverseIndex(idx(ctx));
+			reverseIndex = cache.put(key, POS_REVERSE_INDEX,
+					packDesc.getReverseIndexSize(), revidx);
 			return revidx;
 		}
 	}