[heap] Make Scavenge() private.

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index 415e7d0c5ee569ea458263beb294efc1245cead9..4be2ffe50edc74b8972a3488333b190cd357dc53 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -1681,6 +1681,9 @@ class Heap {
  private:
   Heap();
 
+  // Performs a minor collection in new generation.
+  void Scavenge();
+
   int current_gc_flags() { return current_gc_flags_; }
   void set_current_gc_flags(int flags) {
     current_gc_flags_ = flags;
@@ -2062,9 +2065,6 @@ class Heap {
 
   MUST_USE_RESULT AllocationResult InternalizeString(String* str);
 
-  // Performs a minor collection in new generation.
-  void Scavenge();
-
   // Commits from space if it is uncommitted.
   void EnsureFromSpaceIsCommitted();