Relax test constraints from r15439 (Join threads after stopping).

test/cctest/test-mark-compact.cc

Index: test/cctest/test-mark-compact.cc
diff --git a/test/cctest/test-mark-compact.cc b/test/cctest/test-mark-compact.cc
index 0709704f5e624c70ec535c03ae1a9ced687dc17c..8be72d303a8ad63f989d391c7f146e7226aa23a7 100644
--- a/test/cctest/test-mark-compact.cc
+++ b/test/cctest/test-mark-compact.cc
@@ -581,9 +581,9 @@ intptr_t ShortLivingIsolate() {
 
 
 TEST(RegressJoinThreadsOnIsolateDeinit) {
-  intptr_t first_size = ShortLivingIsolate();
+  intptr_t size_limit = ShortLivingIsolate() * 2;
   for (int i = 0; i < 10; i++) {
-    CHECK_EQ(first_size, ShortLivingIsolate());
+    CHECK_GT(size_limit, ShortLivingIsolate());
   }
 }