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

runtime/vm/dart_entry_test.cc

Index: runtime/vm/dart_entry_test.cc
===================================================================
--- runtime/vm/dart_entry_test.cc	(revision 25321)
+++ runtime/vm/dart_entry_test.cc	(working copy)
@@ -27,9 +27,10 @@
   Library& lib = Library::Handle(Library::CoreLibrary());
   EXPECT_EQ(true, CompilerTest::TestCompileScript(lib, script));
   EXPECT(ClassFinalizer::FinalizePendingClasses());
+  String& ambiguity_error_msg = String::Handle();
   Class& cls = Class::Handle(
-      lib.LookupClass(String::Handle(Symbols::New("A"))));
-  EXPECT(!cls.IsNull());
+      lib.LookupClass(String::Handle(Symbols::New("A")), &ambiguity_error_msg));
+  EXPECT(!cls.IsNull());  // No ambiguity error expected.
   String& name = String::Handle(String::New("foo"));
   Function& function = Function::Handle(cls.LookupStaticFunction(name));
   EXPECT(!function.IsNull());
@@ -55,9 +56,10 @@
   Library& lib = Library::Handle(Library::CoreLibrary());
   EXPECT_EQ(true, CompilerTest::TestCompileScript(lib, script));
   EXPECT(ClassFinalizer::FinalizePendingClasses());
+  String& ambiguity_error_msg = String::Handle();
   Class& cls = Class::Handle(
-      lib.LookupClass(String::Handle(Symbols::New("A"))));
-  EXPECT(!cls.IsNull());
+      lib.LookupClass(String::Handle(Symbols::New("A")), &ambiguity_error_msg));
+  EXPECT(!cls.IsNull());  // No ambiguity error expected.
   String& name = String::Handle(String::New("foo"));
   Function& function = Function::Handle(cls.LookupStaticFunction(name));
   EXPECT(!function.IsNull());
@@ -82,9 +84,10 @@
   Library& lib = Library::Handle(Library::CoreLibrary());
   EXPECT_EQ(true, CompilerTest::TestCompileScript(lib, script));
   EXPECT(ClassFinalizer::FinalizePendingClasses());
+  String& ambiguity_error_msg = String::Handle();
   Class& cls = Class::Handle(
-      lib.LookupClass(String::Handle(Symbols::New("A"))));
-  EXPECT(!cls.IsNull());
+      lib.LookupClass(String::Handle(Symbols::New("A")), &ambiguity_error_msg));
+  EXPECT(!cls.IsNull());  // No ambiguity error expected.
 
   // Invoke the constructor.
   const Instance& instance = Instance::Handle(Instance::New(cls));