Implement --omit, --raw_[context_]file=... for mksnapshot tool.

src/serialize.h

Index: src/serialize.h
diff --git a/src/serialize.h b/src/serialize.h
index 1fc125bcd38188e1540dc532a223a2bea6c061d7..38dfa48973242c337be9644f409e5a4ab9e648d6 100644
--- a/src/serialize.h
+++ b/src/serialize.h
@@ -464,7 +464,7 @@ class Serializer : public SerializerDeserializer {
   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) {
+  int CurrentAllocationAddress(int space) const {
     ASSERT(space < kNumberOfSpaces);
     return fullness_[space];
   }