Refactor resolution code in the vm to properly handle ambiguity errors.

runtime/vm/object_test.cc

Index: runtime/vm/object_test.cc
===================================================================
--- runtime/vm/object_test.cc	(revision 25291)
+++ runtime/vm/object_test.cc	(working copy)
@@ -3223,7 +3223,7 @@
 
 static RawClass* GetClass(const Library& lib, const char* name) {
   const Class& cls =
-      Class::Handle(lib.LookupClass(String::Handle(Symbols::New(name))));
+      Class::Handle(lib.LookupClass(String::Handle(Symbols::New(name)), NULL));
   ASSERT(!cls.IsNull());
   return cls.raw();
 }
@@ -3352,7 +3352,7 @@
   EXPECT(!lib.IsNull());
 
   const Class& class_a = Class::Handle(
-      lib.LookupClass(String::Handle(Symbols::New("A"))));
+      lib.LookupClass(String::Handle(Symbols::New("A")), NULL));
   const Function& test1 = Function::Handle(GetFunction(class_a, "test1"));
   const Function& test2 = Function::Handle(GetFunction(class_a, "test2"));
   const Function& test3 = Function::Handle(GetFunction(class_a, "test3"));