Indicate that low-memory-notificatin triggered GCs are "forced"

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index c918c6793c6a2203bafc713e51fadd5bf055e5b6..50a328a714411a43f110b48f369deb9d11d71d0f 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -797,7 +797,8 @@ void Heap::CollectAllAvailableGarbage(const char* gc_reason) {
   const int kMaxNumberOfAttempts = 7;
   const int kMinNumberOfAttempts = 2;
   for (int attempt = 0; attempt < kMaxNumberOfAttempts; attempt++) {
-    if (!CollectGarbage(MARK_COMPACTOR, gc_reason, NULL) &&
+    if (!CollectGarbage(MARK_COMPACTOR, gc_reason, NULL,
+                        v8::kGCCallbackFlagForced) &&
         attempt + 1 >= kMinNumberOfAttempts) {
       break;
     }