Use the UNIMPLEMENTED macro everywhere.

As suggested in review.

Change-Id: Ic14c91a622b545b4800ef021dfb501fb09cbda9d
diff --git a/src/object.h b/src/object.h
index 1451c54..dfcc626 100644
--- a/src/object.h
+++ b/src/object.h
@@ -167,7 +167,7 @@
   }
 
   bool IsClass() const {
-    LOG(FATAL) << "Unimplemented";
+    UNIMPLEMENTED(FATAL);
     return true;
   }
 
@@ -180,7 +180,7 @@
   }
 
   bool IsObjectArray() const {
-    LOG(FATAL) << "Unimplemented";
+    UNIMPLEMENTED(FATAL);
     return true;
   }
 
@@ -189,32 +189,32 @@
   }
 
   bool IsReference() const {
-    LOG(FATAL) << "Unimplemented";
+    UNIMPLEMENTED(FATAL);
     return true;
   }
 
   bool IsWeakReference() const {
-    LOG(FATAL) << "Unimplemented";
+    UNIMPLEMENTED(FATAL);
     return true;
   }
 
   bool IsSoftReference() const {
-    LOG(FATAL) << "Unimplemented";
+    UNIMPLEMENTED(FATAL);
     return true;
   }
 
   bool IsFinalizerReference() const {
-    LOG(FATAL) << "Unimplemented";
+    UNIMPLEMENTED(FATAL);
     return true;
   }
 
   bool IsPhantomReference() const {
-    LOG(FATAL) << "Unimplemented";
+    UNIMPLEMENTED(FATAL);
     return true;
   }
 
   bool IsArray() const {
-    LOG(FATAL) << "Unimplemented";
+    UNIMPLEMENTED(FATAL);
     return true;
   }