GC: Refactor public incremental marking interface in heap

src/heap/incremental-marking.h

Index: src/heap/incremental-marking.h
diff --git a/src/heap/incremental-marking.h b/src/heap/incremental-marking.h
index 8fe341154fa0597113211ccc7dd8387a350a0c34..2c63cfcad6ade74752f06a6f51bc3cb127e29031 100644
--- a/src/heap/incremental-marking.h
+++ b/src/heap/incremental-marking.h
@@ -26,6 +26,21 @@ class IncrementalMarking {
 
   enum GCRequestType { COMPLETE_MARKING, OVERAPPROXIMATION };
 
+  struct StepActions {
+    StepActions(CompletionAction complete_action_,
+                ForceMarkingAction force_marking_,
+                ForceCompletionAction force_completion_)
+        : completion_action(complete_action_),
+          force_marking(force_marking_),
+          force_completion(force_completion_) {}
+
+    CompletionAction completion_action;
+    ForceMarkingAction force_marking;
+    ForceCompletionAction force_completion;
+  };
+
+  static StepActions NoForcedStepActions();
+
   explicit IncrementalMarking(Heap* heap);
 
   static void Initialize();
@@ -67,7 +82,9 @@ class IncrementalMarking {
 
   bool WasActivated();
 
-  void Start(int mark_compact_flags);
+  void Start(int mark_compact_flags,
+             const GCCallbackFlags gc_callback_flags = kNoGCCallbackFlags,
+             const char* reason = nullptr);
 
   void Stop();
 
@@ -185,6 +202,8 @@ class IncrementalMarking {
 
   Heap* heap() const { return heap_; }
 
+  GCCallbackFlags CallbackFlags() const { return gc_callback_flags_; }
+
  private:
   int64_t SpaceLeftInOldSpace();
 
@@ -243,6 +262,8 @@ class IncrementalMarking {
 
   GCRequestType request_type_;
 
+  GCCallbackFlags gc_callback_flags_;
+
   DISALLOW_IMPLICIT_CONSTRUCTORS(IncrementalMarking);
 };
 }