Add --optimize_for_size to tests flag matrix.

test/cctest/cctest.h

Index: test/cctest/cctest.h
diff --git a/test/cctest/cctest.h b/test/cctest/cctest.h
index 7f84c259f0c4cb1b135ae6a73d465d631d858e31..36621714153d0e81a9a7231aa0fe2402736b5006 100644
--- a/test/cctest/cctest.h
+++ b/test/cctest/cctest.h
@@ -324,7 +324,8 @@ static inline v8::Local<v8::Value> CompileRunWithOrigin(const char* source,
 // Pick a slightly different port to allow tests to be run in parallel.
 static inline int FlagDependentPortOffset() {
   return ::v8::internal::FLAG_crankshaft == false ? 100 :
-         ::v8::internal::FLAG_always_opt ? 200 : 0;
+         ::v8::internal::FLAG_always_opt ? 200 :
+         ::v8::internal::FLAG_optimize_for_size ? 300 : 0;
 }