Add another ifndef and a couple of methods to LruCache

The new methods on LruCache are needed by libhwui to manage
the cache of paths.

Change-Id: If54fa325c54e2b04e7fe5dfe6dad66066c40127c
diff --git a/include/utils/JenkinsHash.h b/include/utils/JenkinsHash.h
index e964e6f..7da5dbd 100644
--- a/include/utils/JenkinsHash.h
+++ b/include/utils/JenkinsHash.h
@@ -19,6 +19,9 @@
  * should still be quite good.
  **/
 
+#ifndef ANDROID_JENKINS_HASH_H
+#define ANDROID_JENKINS_HASH_H
+
 #include <utils/TypeHelpers.h>
 
 namespace android {
@@ -42,3 +45,4 @@
 
 }
 
+#endif // ANDROID_JENKINS_HASH_H