Fixes a couple problems with GC of unoptimized code.

runtime/vm/object.h

Index: runtime/vm/object.h
===================================================================
--- runtime/vm/object.h	(revision 30197)
+++ runtime/vm/object.h	(working copy)
@@ -1997,6 +1997,7 @@
 
   FINAL_HEAP_OBJECT_IMPLEMENTATION(Function, Object);
   friend class Class;
+  friend class RawFunction;
 };
 
 
@@ -3354,6 +3355,10 @@
 
   FINAL_HEAP_OBJECT_IMPLEMENTATION(Code, Object);
   friend class Class;
+
+  // So that the RawFunction pointer visitor can determine whether code the
+  // function points to is optimized.
+  friend class RawFunction;
 };
 
 
@@ -4979,6 +4984,8 @@
   friend class TwoByteString;
   friend class ExternalOneByteString;
   friend class ExternalTwoByteString;
+  // So that the MarkingVisitor can print a debug string from a NoHandleScope.
+  friend class MarkingVisitor;
 };