Explicitly track whether incremental marking was activated

src/heap/incremental-marking.cc

Index: src/heap/incremental-marking.cc
diff --git a/src/heap/incremental-marking.cc b/src/heap/incremental-marking.cc
index 08f11c62799b314f687f55bad6aeac58c34ff843..33f9de0da4b977903103f5fbbaae1bb6b1340e82 100644
--- a/src/heap/incremental-marking.cc
+++ b/src/heap/incremental-marking.cc
@@ -27,7 +27,8 @@ IncrementalMarking::IncrementalMarking(Heap* heap)
       allocated_(0),
       idle_marking_delay_counter_(0),
       no_marking_scope_depth_(0),
-      unscanned_bytes_of_large_object_(0) {}
+      unscanned_bytes_of_large_object_(0),
+      was_activated_(false) {}
 
 
 void IncrementalMarking::RecordWriteSlow(HeapObject* obj, Object** slot,
@@ -423,6 +424,9 @@ bool IncrementalMarking::ShouldActivate() {
 }
 
 
+bool IncrementalMarking::WasActivated() { return was_activated_; }
+
+
 bool IncrementalMarking::WorthActivating() {
 #ifndef DEBUG
   static const intptr_t kActivationThreshold = 8 * MB;
@@ -490,6 +494,8 @@ void IncrementalMarking::Start(CompactionFlag flag) {
 
   ResetStepCounters();
 
+  was_activated_ = true;
+
   if (!heap_->mark_compact_collector()->sweeping_in_progress()) {
     StartMarking(flag);
   } else {
@@ -785,6 +791,9 @@ void IncrementalMarking::MarkingComplete(CompletionAction action) {
 }
 
 
+void IncrementalMarking::Epilogue() { was_activated_ = false; }
+
+
 void IncrementalMarking::OldSpaceStep(intptr_t allocated) {
   if (IsStopped() && ShouldActivate()) {
     // TODO(hpayer): Let's play safe for now, but compaction should be