Make serializer non-static.

src/incremental-marking.cc

Index: src/incremental-marking.cc
diff --git a/src/incremental-marking.cc b/src/incremental-marking.cc
index b726a9bfcc704f4a16f5407d6799e4a2bc93373d..7bce832a0d2fe43d9b2864a50a91651bbc392a1f 100644
--- a/src/incremental-marking.cc
+++ b/src/incremental-marking.cc
@@ -463,7 +463,7 @@ bool IncrementalMarking::WorthActivating() {
   return FLAG_incremental_marking &&
       FLAG_incremental_marking_steps &&
       heap_->gc_state() == Heap::NOT_IN_GC &&
-      !Serializer::enabled(heap_->isolate()) &&
+      !heap_->isolate()->serializer_enabled() &&
       heap_->isolate()->IsInitialized() &&
       heap_->PromotedSpaceSizeOfObjects() > kActivationThreshold;
 }
@@ -541,7 +541,7 @@ void IncrementalMarking::Start(CompactionFlag flag) {
   ASSERT(FLAG_incremental_marking_steps);
   ASSERT(state_ == STOPPED);
   ASSERT(heap_->gc_state() == Heap::NOT_IN_GC);
-  ASSERT(!Serializer::enabled(heap_->isolate()));
+  ASSERT(!heap_->isolate()->serializer_enabled());
   ASSERT(heap_->isolate()->IsInitialized());
 
   ResetStepCounters();