Delay Class parsing until the class is actually used.

runtime/vm/compiler.h

Index: runtime/vm/compiler.h
===================================================================
--- runtime/vm/compiler.h	(revision 23087)
+++ runtime/vm/compiler.h	(working copy)
@@ -24,12 +24,18 @@
 
 class Compiler : public AllStatic {
  public:
-  // Extracts class, interface, function symbols from the script and populates
-  // the symbol tables and the class dictionary of the library.
+  // Extracts top level entities from the script and populates
+  // the class dictionary of the library.
   //
   // Returns Error::null() if there is no compilation error.
   static RawError* Compile(const Library& library, const Script& script);
 
+  // Extracts function and field symbols from the class and populates
+  // the class.
+  //
+  // Returns Error::null() if there is no compilation error.
+  static RawError* CompileClass(const Class& cls);
+
   // Generates code for given function and sets its code field.
   //
   // Returns Error::null() if there is no compilation error.