[heap] Enforce finalization of marking at heap limit when optimizing for memory usage.

BUG=chromium:634900

Review-Url: https://codereview.chromium.org/2225363002
Cr-Commit-Position: refs/heads/master@{#38495}

src/heap/heap-inl.h

@@ -384,7 +384,9 @@ bool Heap::InOldSpaceSlow(Address address) {
 }
 
 bool Heap::OldGenerationAllocationLimitReached() {
-  if (!incremental_marking()->IsStopped()) return false;
+  if (!incremental_marking()->IsStopped() && !ShouldOptimizeForMemoryUsage()) {
+    return false;
+  }
   return OldGenerationSpaceAvailable() < 0;
 }