ART: Ensure SlowDebug is enabled in all gtests

This was missed when moving to common_art_test.

Test: m test-art-gtest
Change-Id: I0ff50983cf71bd86b32350222caac2a36a72ad4b
diff --git a/runtime/common_runtime_test.cc b/runtime/common_runtime_test.cc
index 46240d4..05ec9e6 100644
--- a/runtime/common_runtime_test.cc
+++ b/runtime/common_runtime_test.cc
@@ -122,6 +122,8 @@
   options.push_back(std::make_pair("-Xcheck:jni", nullptr));
   options.push_back(std::make_pair(min_heap_string, nullptr));
   options.push_back(std::make_pair(max_heap_string, nullptr));
+
+  // Technically this is redundant w/ common_art_test, but still check.
   options.push_back(std::make_pair("-XX:SlowDebug=true", nullptr));
   static bool gSlowDebugTestFlag = false;
   RegisterRuntimeDebugFlag(&gSlowDebugTestFlag);