Add some interfaces to the GC that allow us to reserve space. This is needed...

src/serialize.h

Index: src/serialize.h
===================================================================
--- src/serialize.h	(revision 3575)
+++ src/serialize.h	(working copy)
@@ -199,7 +199,8 @@
     SYNCHRONIZE = 36,
     START_NEW_PAGE_SERIALIZATION = 37,
     NATIVES_STRING_RESOURCE = 38,
-    // Free: 39-47.
+    ROOT_SERIALIZATION = 39,
+    // Free: 40-47.
     BACKREF_SERIALIZATION = 48,
     // One per space, must be kSpaceMask aligned.
     // Free: 57-63.
@@ -293,10 +294,17 @@
 class Serializer : public SerDes {
  public:
   explicit Serializer(SnapshotByteSink* sink);
-  // Serialize the current state of the heap. This operation destroys the
-  // heap contents.
+  // Serialize the current state of the heap.
   void Serialize();
+  // Serialize a single object and the objects reachable from it.
+  void SerializePartial(Object** obj);
   void VisitPointers(Object** start, Object** end);
+  // You can call this after serialization to find out how much space was used
+  // in each space.
+  int CurrentAllocationAddress(int space) {
+    if (SpaceIsLarge(space)) space = LO_SPACE;
+    return fullness_[space];
+  }
 
   static void Enable() {
     if (!serialization_enabled_) {
@@ -366,13 +374,11 @@
   // once the map has been used for the serialization address.
   static int SpaceOfAlreadySerializedObject(HeapObject* object);
   int Allocate(int space, int size, bool* new_page_started);
-  int CurrentAllocationAddress(int space) {
-    if (SpaceIsLarge(space)) space = LO_SPACE;
-    return fullness_[space];
-  }
   int EncodeExternalReference(Address addr) {
     return external_reference_encoder_->Encode(addr);
   }
+  int RootIndex(HeapObject* heap_object);
+  static const int kInvalidRootIndex = -1;
 
   // Keep track of the fullness of each space in order to generate
   // relative addresses for back references.  Large objects are
@@ -382,6 +388,7 @@
   SnapshotByteSink* sink_;
   int current_root_index_;
   ExternalReferenceEncoder* external_reference_encoder_;
+  bool partial_;
   static bool serialization_enabled_;
   // Did we already make use of the fact that serialization was not enabled?
   static bool too_late_to_enable_now_;