Use Map.Entry, not HashMap.Entry

Map.Entry is the defined return value from entrySet().  HashMap.Entry
shouldn't be used directly.

Change-Id: I855f7a4e855776deb83754ca89c2a4128e9e04a2

src/com/android/email/provider/ContentCache.java

@@ -167,7 +167,7 @@ public final class ContentCache {
         /**
          * For Debugging Only - not efficient
          */
-        synchronized Set<HashMap.Entry<T, Integer>> entrySet() {
+        synchronized Set<Map.Entry<T, Integer>> entrySet() {
             return mMap.entrySet();
         }
     }