Another round of cleanups for http://www.dartbug.com/15922

runtime/vm/object.h

Index: runtime/vm/object.h
===================================================================
--- runtime/vm/object.h	(revision 32732)
+++ runtime/vm/object.h	(working copy)
@@ -4024,7 +4024,7 @@
   void SetFieldAtOffset(intptr_t offset, const Object& value) const {
     StorePointer(FieldAddrAtOffset(offset), value.raw());
   }
-  bool IsValidFieldOffset(int offset) const;
+  bool IsValidFieldOffset(intptr_t offset) const;
 
   static intptr_t NextFieldOffset() {
     return sizeof(RawInstance);
@@ -5634,7 +5634,7 @@
   // 'source' to the new array. 'new_length' must be greater than or equal to
   // 'source.Length()'. 'source' can be null.
   static RawArray* Grow(const Array& source,
-                        int new_length,
+                        intptr_t new_length,
                         Heap::Space space = Heap::kNew);
 
   // Return an Array object that contains all the elements currently present