Implement override checks.

dart/tests/language/language_dart2js.status

Index: dart/tests/language/language_dart2js.status
diff --git a/dart/tests/language/language_dart2js.status b/dart/tests/language/language_dart2js.status
index 08de51960aaa045f2b9f4efb258e0e45a8ce5b6a..ed5ddd0891b051cb5851e459a11a9aebeab13096 100644
--- a/dart/tests/language/language_dart2js.status
+++ b/dart/tests/language/language_dart2js.status
@@ -34,7 +34,6 @@ arithmetic_test: Fail
 assertion_test: Fail, OK
 
 [ $compiler == dart2js ]
-fauxverride_test/05: Fail # TODO(ahe): I have a pending CL for this.
 compile_time_constant8_test: Fail # We don't take the generic type into account yet.
 static_initializer_type_error_test: Fail # Checked mode not supported.
 exception_test: Fail # "throw null" throws NullPointerException.
@@ -166,8 +165,7 @@ override_field_method1_negative_test: Fail, OK # Negative language test.
 override_field_method2_negative_test: Fail, OK # Negative language test.
 override_field_method3_negative_test: Fail, OK # Negative language test.
 override_field_method6_negative_test: Fail, OK # Negative language test.
-override_field_test/01: Fail, OK # Negative language test.
-override_field_test/04: Fail, OK # Negative language test.
+override_field_test/04: Fail, OK # Broken test.
 override_method_with_field_test/01: Fail, OK # Negative language test.
 prefix16_test: Fail
 prefix18_negative_test: Fail, OK # Negative language test.
@@ -231,7 +229,6 @@ assign_top_method_negative_test: Crash
 
 
 [ $compiler == dart2js && ($runtime == ff || $runtime == safari || $runtime == d8 || $runtime == drt || $runtime == chrome) ]
-class_override_negative_test: Fail, OK # Negative language test.
 override_field_method4_negative_test: Fail, OK # Negative language test.
 override_field_method5_negative_test: Fail, OK # Negative language test.