Make the speed of incrmental marking depend also on the rate

src/incremental-marking.h

Index: src/incremental-marking.h
===================================================================
--- src/incremental-marking.h	(revision 12583)
+++ src/incremental-marking.h	(working copy)
@@ -95,21 +95,22 @@
   // progress in the face of the mutator creating new work for it.  We start
   // of at a moderate rate of work and gradually increase the speed of the
   // incremental marker until it completes.
-  // Do some marking every time this much memory has been allocated.
-  static const intptr_t kAllocatedThreshold = 65536;
+  // Do some marking every time this much memory has been allocated or this many
+  // heavy (color-checking) write barriers have been invoked.
+  static const intptr_t kIncrementalMarkingThreshold = 65536;
   // Start off by marking this many times more memory than has been allocated.
-  static const intptr_t kInitialAllocationMarkingFactor = 1;
+  static const intptr_t kInitialMarkingSpeed = 1;
   // But if we are promoting a lot of data we need to mark faster to keep up
   // with the data that is entering the old space through promotion.
   static const intptr_t kFastMarking = 3;
   // After this many steps we increase the marking/allocating factor.
-  static const intptr_t kAllocationMarkingFactorSpeedupInterval = 1024;
+  static const intptr_t kMarkingSpeedAccellerationInterval = 1024;
   // This is how much we increase the marking/allocating factor by.
-  static const intptr_t kAllocationMarkingFactorSpeedup = 2;
-  static const intptr_t kMaxAllocationMarkingFactor = 1000;
+  static const intptr_t kMarkingSpeedAccelleration = 2;
+  static const intptr_t kMaxMarkingSpeed = 1000;
 
   void OldSpaceStep(intptr_t allocated) {
-    Step(allocated * kFastMarking / kInitialAllocationMarkingFactor,
+    Step(allocated * kFastMarking / kInitialMarkingSpeed,
          GC_VIA_STACK_GUARD);
   }
 
@@ -211,13 +212,13 @@
 
   void NotifyOfHighPromotionRate() {
     if (IsMarking()) {
-      if (allocation_marking_factor_ < kFastMarking) {
+      if (marking_speed_ < kFastMarking) {
         if (FLAG_trace_gc) {
           PrintPID("Increasing marking speed to %d "
                    "due to high promotion rate\n",
                    static_cast<int>(kFastMarking));
         }
-        allocation_marking_factor_ = kFastMarking;
+        marking_speed_ = kFastMarking;
       }
     }
   }
@@ -275,9 +276,10 @@
   double steps_took_since_last_gc_;
   int64_t bytes_rescanned_;
   bool should_hurry_;
-  int allocation_marking_factor_;
+  int marking_speed_;
   intptr_t bytes_scanned_;
   intptr_t allocated_;
+  intptr_t write_barriers_invoked_since_last_step_;
 
   int no_marking_scope_depth_;