Add BlameCacheImpl.Key.toString()

Change-Id: I1e9e51fc8723e3aab6c05a7497296caa0f594641

gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameCacheImpl.java

diff --git a/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameCacheImpl.java b/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameCacheImpl.java
index 768e8e5..459bccd 100644
--- a/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameCacheImpl.java
+++ b/gitiles-servlet/src/main/java/com/google/gitiles/blame/BlameCacheImpl.java
@@ -31,6 +31,7 @@
 import org.eclipse.jgit.lib.ObjectId;
 import org.eclipse.jgit.lib.PersonIdent;
 import org.eclipse.jgit.lib.Repository;
+import org.eclipse.jgit.util.QuotedString;
 
 import java.io.IOException;
 import java.util.Collections;
@@ -87,6 +88,11 @@
     public int hashCode() {
       return Objects.hashCode(commitId, path);
     }
+
+    @Override
+    public String toString() {
+      return commitId.name() + ":" + QuotedString.GIT_PATH.quote(path);
+    }
   }
 
   private final LoadingCache<Key, List<Region>> cache;