[heap] Add page evacuation mode for new->new

src/heap/spaces.h

Index: src/heap/spaces.h
diff --git a/src/heap/spaces.h b/src/heap/spaces.h
index fbbd9da8dff89812fc38f318e48a99e161d58503..130e2dd134180eb246665b199af3a7a3361e34ad 100644
--- a/src/heap/spaces.h
+++ b/src/heap/spaces.h
@@ -425,6 +425,10 @@ class MemoryChunk {
     // from new to old space during evacuation.
     PAGE_NEW_OLD_PROMOTION,
 
+    // |PAGE_NEW_NEW_PROMITION|: A page tagged with this flag has been moved
+    // within the new space during evacuation.
+    PAGE_NEW_NEW_PROMOTION,
+
     // A black page has all mark bits set to 1 (black). A black page currently
     // cannot be iterated because it is not swept. Moreover live bytes are also
     // not updated.
@@ -2440,6 +2444,8 @@ class SemiSpace : public Space {
   Page* first_page() { return anchor_.next_page(); }
   Page* current_page() { return current_page_; }
 
+  bool OnLastPage() { return current_page() == anchor()->prev_page(); }
+
   // Returns one past the end address of the space.
   Address space_end() { return anchor_.prev_page()->area_end(); }
 
@@ -2460,6 +2466,7 @@ class SemiSpace : public Space {
   void Reset();
 
   bool ReplaceWithEmptyPage(Page* page);
+  void PrependPage(Page* page);
 
   // Age mark accessors.
   Address age_mark() { return age_mark_; }
@@ -2721,6 +2728,13 @@ class NewSpace : public Space {
     return from_space_.ReplaceWithEmptyPage(page);
   }
 
+  void AddPageToToSpace(Page* page) {
+    DCHECK(page->InFromSpace());
+    DCHECK(!to_space_.OnLastPage());
+    to_space_.PrependPage(page);
+    pages_used_++;
+  }
+
   // Return the maximum capacity of a semispace.
   int MaximumCapacity() {
     DCHECK(to_space_.maximum_capacity() == from_space_.maximum_capacity());