Add memory pressure notification API

src/api.cc

Index: src/api.cc
diff --git a/src/api.cc b/src/api.cc
index 647bd6e21bca049e94c62ce8cea89a8605acbe71..37a87985dec5f2b26c1fa35a0784eacd8addb524 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(level,
+                                                     Locker::IsLocked(this));

[jochen (gone - plz use gerrit), 2016/03/18 15:29:12]

as explained offline, Locker::IsLocked() always returns false in blink (as it
doesn't use lockers).

in general, we can't know whether the "main" thread is running JS currently
(without races), so I'd recommend to set the interrupt flag and internally
schedule a task using PostTaskOnForegroundThread() to make sure that the
interrupt flag actually gets honored.

[ulan, 2016/03/18 16:10:00]

Done.

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