[heap] Reland "Use RAIL mode for initial heap sizing"

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 3c4057373906527ea89e862069d868f57b63932a..c5bab7c350db35ea5d764dfb4a60589e1815a3ee 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -1848,6 +1848,14 @@ class Heap {
   // Growing strategy. =========================================================
   // ===========================================================================
 
+  // For some webpages RAIL mode does not switch from PERFORMANCE_LOAD.
+  // This constant limits the effect of load RAIL mode on GC.
+  // The value is arbitrary and chosen as the largest load time observed in
+  // v8 browsing benchmarks.
+  static const int kMaxLoadTimeMs = 3000;
+
+  bool ShouldOptimizeForLoadTime();
+
   // Decrease the allocation limit if the new limit based on the given
   // parameters is lower than the current limit.
   void DampenOldGenerationAllocationLimit(size_t old_gen_size, double gc_speed,