Relax test condition to make it less brittle.

test/cctest/test-heap.cc

Index: test/cctest/test-heap.cc
diff --git a/test/cctest/test-heap.cc b/test/cctest/test-heap.cc
index da3ccb9273c0557ac39f6485d521dd166f9aebb0..014eefb5bebfc3012cdbecbf9a5a46e15be4e1bd 100644
--- a/test/cctest/test-heap.cc
+++ b/test/cctest/test-heap.cc
@@ -1290,7 +1290,8 @@ TEST(CollectingAllAvailableGarbageShrinksNewSpace) {
   CHECK(old_capacity == new_capacity);
 }
 
-
+// This just checks the contract of the IdleNotification() function,
+// and does not verify that it does reasonable work.
 TEST(IdleNotificationAdvancesIncrementalMarking) {
   if (!FLAG_incremental_marking || !FLAG_incremental_marking_steps) return;
   InitializeVM();
@@ -1315,5 +1316,5 @@ TEST(IdleNotificationAdvancesIncrementalMarking) {
   bool no_idle_work = v8::V8::IdleNotification(900);
   while (!v8::V8::IdleNotification(900)) ;
   intptr_t new_size = HEAP->SizeOfObjects();
-  CHECK(no_idle_work || new_size < 3 * old_size / 4);
+  CHECK(no_idle_work || new_size < old_size);
 }