Unify memory optimization modes and flags.

src/isolate.cc

Index: src/isolate.cc
diff --git a/src/isolate.cc b/src/isolate.cc
index c006d6f46b73ae20c9b13a26aa0d1af6afe10ade..859d91381b1c290b2b14a9523656739a82bef2e7 100644
--- a/src/isolate.cc
+++ b/src/isolate.cc
@@ -1998,6 +1998,7 @@ Isolate::Isolate(bool enable_serializer)
       has_fatal_error_(false),
       initialized_from_snapshot_(false),
       is_tail_call_elimination_enabled_(true),
+      is_isolate_in_background_(false),
       cpu_profiler_(NULL),
       heap_profiler_(NULL),
       code_event_dispatcher_(new CodeEventDispatcher()),
@@ -3172,6 +3173,15 @@ void Isolate::SetRAILMode(RAILMode rail_mode) {
   }
 }
 
+void Isolate::IsolateInBackgroundNotification() {
+  is_isolate_in_background_ = false;
+  heap()->ActivateMemoryReducerIfNeeded();
+}
+
+void Isolate::IsolateInForegroundNotification() {
+  is_isolate_in_background_ = true;
+}
+
 bool StackLimitCheck::JsHasOverflowed(uintptr_t gap) const {
   StackGuard* stack_guard = isolate_->stack_guard();
 #ifdef USE_SIMULATOR