Add memory pressure notification API

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 647bd6e21bca049e94c62ce8cea89a8605acbe71..793b53016f62184c4bdeb0403d0d12308531646c 100644
--- a/src/api.cc
+++ b/src/api.cc
@@ -7586,6 +7586,11 @@ void Isolate::IsolateInBackgroundNotification() {
   return isolate->heap()->SetOptimizeForMemoryUsage();
 }
 
+void Isolate::MemoryPressureNotification(MemoryPressureLevel level) {
+  i::Isolate* isolate = reinterpret_cast<i::Isolate*>(this);
+  return isolate->heap()->MemoryPressureNotification(
+      static_cast<i::MemoryPressureLevel>(level), Locker::IsLocked(this));

[jochen (gone - plz use gerrit), 2016/03/17 19:33:39]

IsLocked() should never be true in blink, right?

[ulan, 2016/03/18 12:49:40]

If V8 is not executing JS code and there is memory pressure event in chrome,
then it would be optimal to enter the isolate and then call the function. That
way we can do GC immediately.  Otherwise, the notification will have no effect
until V8 starts running.

+}
 
 void Isolate::SetJitCodeEventHandler(JitCodeEventOptions options,
                                      JitCodeEventHandler event_handler) {