Tidy up some C-isms.

Change-Id: I53b457cab9067369320457549071fc3e4c23c81b
diff --git a/src/runtime.cc b/src/runtime.cc
index 25789ab..37887e2 100644
--- a/src/runtime.cc
+++ b/src/runtime.cc
@@ -818,7 +818,7 @@
   case KIND_EXT_FREED_BYTES:
     return 0;  // backward compatibility
   default:
-    CHECK(false);
+    LOG(FATAL) << "Unknown statistic " << kind;
     return -1; // unreachable
   }
 }