Add memory pressure notification API

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 44a080b1e0914ddbd9c40772bcd7d2cc03c3b393..4694ffb459d46acb9862a9ab0ec31955c123b343 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -10,6 +10,7 @@
 
 // Clients of this interface shouldn't depend on lots of heap internals.
 // Do not include anything from src/heap here!
+#include "include/v8.h"
 #include "src/allocation.h"
 #include "src/assert-scope.h"
 #include "src/atomic-utils.h"
@@ -23,6 +24,8 @@
 namespace v8 {
 namespace internal {
 
+using v8::MemoryPressureLevel;
+
 // Defines all the roots in Heap.
 #define STRONG_ROOT_LIST(V)                                                    \
   V(Map, byte_array_map, ByteArrayMap)                                         \
@@ -736,6 +739,9 @@ class Heap {
   bool IdleNotification(double deadline_in_seconds);
   bool IdleNotification(int idle_time_in_ms);
 
+  void MemoryPressureNotification(MemoryPressureLevel level,
+                                  bool is_isolate_locked);
+
   double MonotonicallyIncreasingTimeInMs();
 
   void RecordStats(HeapStats* stats, bool take_snapshot = false);
@@ -750,6 +756,9 @@ class Heap {
 
     if (PromotedTotalSize() >= adjusted_allocation_limit) return true;
 
+    if (memory_pressure_level_.Value() != MemoryPressureLevel::kNone)
+      return true;
+
     return false;
   }
 
@@ -833,7 +842,10 @@ class Heap {
 
   void SetOptimizeForLatency() { optimize_for_memory_usage_ = false; }
   void SetOptimizeForMemoryUsage();
-  bool ShouldOptimizeForMemoryUsage() { return optimize_for_memory_usage_; }
+  bool ShouldOptimizeForMemoryUsage() {
+    return optimize_for_memory_usage_ ||
+           memory_pressure_level_.Value() != MemoryPressureLevel::kNone;
+  }
 
   // ===========================================================================
   // Initialization. ===========================================================
@@ -1996,6 +2008,8 @@ class Heap {
   // count, as scopes can be acquired from multiple tasks (read: threads).
   AtomicNumber<size_t> always_allocate_scope_count_;
 
+  AtomicValue<MemoryPressureLevel> memory_pressure_level_;

[Hannes Payer (out of office), 2016/03/18 13:27:26]

For completeness, add a comment to describe that field.

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

Done.

+
   // For keeping track of context disposals.
   int contexts_disposed_;