Delay Class parsing until the class is actually used.

runtime/vm/raw_object.h

Index: runtime/vm/raw_object.h
===================================================================
--- runtime/vm/raw_object.h	(revision 22914)
+++ runtime/vm/raw_object.h	(working copy)
@@ -458,7 +458,7 @@
   enum ClassState {
     kAllocated,     // Initial state.
     kPreFinalized,  // VM classes: size precomputed, but no checks done.
-    kFinalized,     // All checks completed, class ready for use.
+    kFinalized,     // Class parsed, finalized and ready for use.
   };
 
  private:
@@ -476,6 +476,7 @@
   RawTypeArguments* type_parameters_;  // Array of TypeParameter.
   RawAbstractType* super_type_;
   RawType* mixin_;
+  RawGrowableObjectArray* patch_classes_;
   RawFunction* signature_function_;  // Associated function for signature class.
   RawArray* constants_;  // Canonicalized values of this class.
   RawArray* canonical_types_;  // Canonicalized types of this class.
@@ -491,7 +492,7 @@
   intptr_t next_field_offset_in_words_;  // Offset of the next instance field.
   intptr_t num_native_fields_;  // Number of native fields in class.
   intptr_t token_pos_;
-  uint8_t state_bits_;  // state, is_const, is_implemented.
+  uint16_t state_bits_;  // state, is_const, is_implemented, needs_parsing.
 
   friend class Instance;
   friend class Object;