Shrink the new space and uncommit marking deque on low memory notification.

src/heap.cc

Index: src/heap.cc
diff --git a/src/heap.cc b/src/heap.cc
index ef1eb77a500ab4c9916506c13e1295d9fb0a9555..4da83e859e3ddff3f2988c00f066ab63ddf58c04 100644
--- a/src/heap.cc
+++ b/src/heap.cc
@@ -447,6 +447,7 @@ void Heap::CollectAllAvailableGarbage() {
   // hope that eventually there will be no weak callbacks invocations.
   // Therefore stop recollecting after several attempts.
   mark_compact_collector()->SetFlags(kMakeHeapIterableMask);
+  isolate_->compilation_cache()->Clear();
   const int kMaxNumberOfAttempts = 7;
   for (int attempt = 0; attempt < kMaxNumberOfAttempts; attempt++) {
     if (!CollectGarbage(OLD_POINTER_SPACE, MARK_COMPACTOR)) {
@@ -454,6 +455,8 @@ void Heap::CollectAllAvailableGarbage() {
     }
   }
   mark_compact_collector()->SetFlags(kNoGCFlags);
+  new_space_.Shrink();
+  incremental_marking()->UncommitMarkingDeque();
 }