Last snapshot bits to get working precompiled hello_world on x64.

runtime/vm/pages.h

Index: runtime/vm/pages.h
diff --git a/runtime/vm/pages.h b/runtime/vm/pages.h
index cb5c1dc2b8b511b3ff4c6669f0b9f95b7b5a837c..e67bc812f0e7c842336d5c48bb3c1a3d5609db25 100644
--- a/runtime/vm/pages.h
+++ b/runtime/vm/pages.h
@@ -42,7 +42,7 @@ class HeapPage {
   }
 
   uword object_start() const {
-    return (reinterpret_cast<uword>(this) + ObjectStartOffset());
+    return memory_->start() + ObjectStartOffset();
   }
   uword object_end() const {
     return object_end_;
@@ -340,6 +340,8 @@ class PageSpace {
   static intptr_t top_offset() { return OFFSET_OF(PageSpace, bump_top_); }
   static intptr_t end_offset() { return OFFSET_OF(PageSpace, bump_end_); }
 
+  void SetupInstructionsSnapshotPage(void* pointer, uword size);
+
  private:
   // Ids for time and data records in Heap::GCStats.
   enum {