Revert of Allow compaction when incremental marking is on.

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 f2ce5e155f5f80c1b92fa91724d6d11ac0ede04f..56cd688446ba92f3d568b60164bcc91bb612dade 100644
--- a/src/heap/incremental-marking.cc
+++ b/src/heap/incremental-marking.cc
@@ -459,7 +459,7 @@
 }
 
 
-void IncrementalMarking::Start() {
+void IncrementalMarking::Start(CompactionFlag flag) {
   if (FLAG_trace_incremental_marking) {
     PrintF("[IncrementalMarking] Start\n");
   }
@@ -474,7 +474,7 @@
   was_activated_ = true;
 
   if (!heap_->mark_compact_collector()->sweeping_in_progress()) {
-    StartMarking();
+    StartMarking(flag);
   } else {
     if (FLAG_trace_incremental_marking) {
       PrintF("[IncrementalMarking] Start sweeping.\n");
@@ -486,12 +486,12 @@
 }
 
 
-void IncrementalMarking::StartMarking() {
+void IncrementalMarking::StartMarking(CompactionFlag flag) {
   if (FLAG_trace_incremental_marking) {
     PrintF("[IncrementalMarking] Start marking\n");
   }
 
-  is_compacting_ = !FLAG_never_compact &&
+  is_compacting_ = !FLAG_never_compact && (flag == ALLOW_COMPACTION) &&
                    heap_->mark_compact_collector()->StartCompaction(
                        MarkCompactCollector::INCREMENTAL_COMPACTION);
 
@@ -823,7 +823,9 @@
 
 void IncrementalMarking::OldSpaceStep(intptr_t allocated) {
   if (IsStopped() && ShouldActivate()) {
-    Start();
+    // TODO(hpayer): Let's play safe for now, but compaction should be
+    // in principle possible.
+    Start(PREVENT_COMPACTION);
   } else {
     Step(allocated * kFastMarking / kInitialMarkingSpeed, GC_VIA_STACK_GUARD);
   }
@@ -952,7 +954,7 @@
       }
       if (!heap_->mark_compact_collector()->sweeping_in_progress()) {
         bytes_scanned_ = 0;
-        StartMarking();
+        StartMarking(PREVENT_COMPACTION);
       }
     } else if (state_ == MARKING) {
       bytes_processed = ProcessMarkingDeque(bytes_to_process);