- Allow for experimentation with different header sizes.

runtime/vm/object.h

Index: runtime/vm/object.h
===================================================================
--- runtime/vm/object.h	(revision 21320)
+++ runtime/vm/object.h	(working copy)
@@ -4144,7 +4144,8 @@
   // All strings share the same maximum element count to keep things
   // simple.  We choose a value that will prevent integer overflow for
   // 2 byte strings, since it is the worst case.
-  static const intptr_t kSizeofRawString = sizeof(RawObject) + (2 * kWordSize);
+  static const intptr_t kSizeofRawString =
+      sizeof(RawInstance) + (2 * kWordSize);
   static const intptr_t kMaxElements = kSmiMax / kTwoByteChar;
 
   class CodePointIterator : public ValueObject {
@@ -4789,7 +4790,7 @@
 
   static intptr_t InstanceSize(intptr_t len) {
     // Ensure that variable length data is not adding to the object length.
-    ASSERT(sizeof(RawArray) == (sizeof(RawObject) + (2 * kWordSize)));
+    ASSERT(sizeof(RawArray) == (sizeof(RawInstance) + (2 * kWordSize)));
     ASSERT(0 <= len && len <= kMaxElements);
     return RoundedAllocationSize(sizeof(RawArray) + (len * kBytesPerElement));
   }