Add memory pressure notification API

include/v8.h

Index: include/v8.h
diff --git a/include/v8.h b/include/v8.h
index ab945ec5324085af75656b9a8156165eeef548b0..db2178b73becb2c7ad76a5f28e8b81e4c14d1c33 100644
--- a/include/v8.h
+++ b/include/v8.h
@@ -5350,6 +5350,15 @@ class V8_EXPORT PersistentHandleVisitor {  // NOLINT
                                      uint16_t class_id) {}
 };
 
+/**
+ * Memory pressure level for the MemoryPressureNotification.
+ * kNone hints V8 that there is no memory pressure.
+ * kModerate hints V8 to speed up incremental garbage collection at the cost of
+ * of higher latency due to garbage collection pauses.
+ * kCritical hints V8 to free memory as soon as possible. Garbage collection
+ * pauses at this level will be large.
+ */
+enum class MemoryPressureLevel { kNone, kModerate, kCritical };
 
 /**
  * Isolate represents an isolated instance of the V8 engine.  V8 isolates have
@@ -5591,6 +5600,14 @@ class V8_EXPORT Isolate {
       AbortOnUncaughtExceptionCallback callback);
 
   /**
+   * Optional notification that the system is running low on memory.
+   * V8 uses these notifications to guide heuristics.
+   * It is allowed to call this function from another thread while
+   * the isolate is executing long running JavaScript code.
+   */
+  void MemoryPressureNotification(MemoryPressureLevel level);
+
+  /**
    * Methods below this point require holding a lock (using Locker) in
    * a multi-threaded environment.
    */