Make full GC reduce memory footprint an explicit event in the idle notification handler.

src/heap/heap.cc

Index: src/heap/heap.cc
diff --git a/src/heap/heap.cc b/src/heap/heap.cc
index 1fe546386ba8d8baa5c452f87a218a19a2111781..e97a5a17e6f30f138ec846254323ec966bf0b3a8 100644
--- a/src/heap/heap.cc
+++ b/src/heap/heap.cc
@@ -4533,14 +4533,15 @@ void Heap::MakeHeapIterable() {
 }
 
 
-void Heap::IdleMarkCompact(const char* message) {
+void Heap::IdleMarkCompact(bool reduce_memory, const char* message) {
   bool uncommit = false;
   if (gc_count_at_last_idle_gc_ == gc_count_) {
     // No GC since the last full GC, the mutator is probably not active.
     isolate_->compilation_cache()->Clear();
     uncommit = true;
   }
-  CollectAllGarbage(kReduceMemoryFootprintMask, message);
+  int flags = reduce_memory ? kReduceMemoryFootprintMask : kNoGCFlags;
+  CollectAllGarbage(flags, message);
   gc_idle_time_handler_.NotifyIdleMarkCompact();
   gc_count_at_last_idle_gc_ = gc_count_;
   if (uncommit) {
@@ -4672,10 +4673,14 @@ bool Heap::IdleNotification(double deadline_in_seconds) {
         gc_idle_time_handler_.NotifyIdleMarkCompact();
         gc_count_at_last_idle_gc_ = gc_count_;
       } else {
-        IdleMarkCompact("idle notification: finalize idle round");
+        IdleMarkCompact(false, "idle notification: finalize idle round");
       }
       break;
     }
+    case DO_FULL_GC_COMPACT: {
+      IdleMarkCompact(true, "idle notification: reduce memory footprint");
+      break;
+    }
     case DO_SCAVENGE:
       CollectGarbage(NEW_SPACE, "idle notification: scavenge");
       break;