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

runtime/vm/code_generator_test.cc

Index: runtime/vm/code_generator_test.cc
===================================================================
--- runtime/vm/code_generator_test.cc	(revision 25321)
+++ runtime/vm/code_generator_test.cc	(working copy)
@@ -272,7 +272,8 @@
 
 static RawClass* LookupClass(const Library& lib, const char* name) {
   const String& cls_name = String::ZoneHandle(Symbols::New(name));
-  return lib.LookupClass(cls_name);
+  String& ambiguity_error_msg = String::Handle();
+  return lib.LookupClass(cls_name, &ambiguity_error_msg);
 }
 
 
@@ -292,7 +293,7 @@
   EXPECT(CompilerTest::TestCompileScript(lib, script));
   EXPECT(ClassFinalizer::FinalizePendingClasses());
   Class& cls = Class::Handle(LookupClass(lib, "A"));
-  EXPECT(!cls.IsNull());
+  EXPECT(!cls.IsNull());  // No ambiguity error expected.
 
   // 'bar' will not be compiled.
   String& function_bar_name = String::Handle(String::New("bar"));
@@ -339,7 +340,7 @@
   EXPECT(CompilerTest::TestCompileScript(lib, script));
   EXPECT(ClassFinalizer::FinalizePendingClasses());
   Class& cls = Class::ZoneHandle(LookupClass(lib, "A"));
-  EXPECT(!cls.IsNull());
+  EXPECT(!cls.IsNull());  // No ambiguity error expected.
 
   String& constructor_name = String::Handle(String::New("A."));
   Function& constructor =
@@ -525,7 +526,7 @@
   EXPECT(CompilerTest::TestCompileScript(lib, script));
   EXPECT(ClassFinalizer::FinalizePendingClasses());
   Class& cls = Class::ZoneHandle(LookupClass(lib, "A"));
-  EXPECT(!cls.IsNull());
+  EXPECT(!cls.IsNull());  // No ambiguity error expected.
 
   String& constructor_name = String::Handle(String::New("A."));
   Function& constructor =
@@ -551,9 +552,11 @@
   Library& app_lib = Library::Handle();
   app_lib ^= libs.At(num_libs - 1);
   ASSERT(!app_lib.IsNull());
+  String& ambiguity_error_msg = String::Handle();
   const Class& cls = Class::Handle(
-      app_lib.LookupClass(String::Handle(Symbols::New("A"))));
-  EXPECT_EQ(cls.raw(), result.clazz());
+      app_lib.LookupClass(String::Handle(Symbols::New("A")),
+                          &ambiguity_error_msg));
+  EXPECT_EQ(cls.raw(), result.clazz());  // No ambiguity error expected.
 }
 
 }  // namespace dart