[heap] Minor MC: Add evacuation phase

src/heap/heap.h

Index: src/heap/heap.h
diff --git a/src/heap/heap.h b/src/heap/heap.h
index f29ba6b9687690e6a611658190299c1352ae614d..c01ce7cf4a1d35373be29e60193d474a68ba5a09 100644
--- a/src/heap/heap.h
+++ b/src/heap/heap.h
@@ -2400,7 +2400,6 @@ class AlwaysAllocateScope {
   Heap* heap_;
 };
 
-
 // Visitor class to verify interior pointers in spaces that do not contain
 // or care about intergenerational references. All heap object pointers have to
 // point into the heap to a location that has a map pointer at its first word.
@@ -2529,7 +2528,6 @@ class WeakObjectRetainer {
   virtual Object* RetainAs(Object* object) = 0;
 };
 
-
 #ifdef DEBUG
 // Helper class for tracing paths to a search target Object from all roots.
 // The TracePathFrom() method can be used to trace paths from a specific