Implement constant maps with __proto__ and fix maps with duplicated keys.

tests/language/language.status

 # Copyright (c) 2012, the Dart project authors.  Please see the AUTHORS file
 # for details. All rights reserved. Use of this source code is governed by a
 # BSD-style license that can be found in the LICENSE file.
 
 # This directory contains tests that are intended to show the
 # current state of the language.
 
 # In order to maintain maximum test coverage for all builds,
 # please use the following procedure to mark a test
 # failed on architectures other than the one you are working on.
@@ skipping 204 matching lines @@
 
 [ $compiler == frog  || $compiler == frogsh ]
 ExceptionTest: Fail # Issue 1785
 Factory3Test: Fail # Issue 417
 Factory2NegativeTest: Fail
 CallThroughNullGetterTest: Fail # Throw ObjectNotClosure instead of NullPointerException.
 CompileTimeConstantCTest/02: Fail # string-concatenated (+) keys in literal maps.
 CompileTimeConstantDTest: Fail # doesn't recognize 400 + z (with z parameter of constructor) as compile-time constant.
 CompileTimeConstantETest: Fail
 CompileTimeConstantGTest: Fail # compile time constants with super calls to optional arguments.
+CompileTimeConstantKTest: Fail # Constant maps are not canonicalized correctly if the same key appears multiple times.
 DisablePrivacyTest: Skip  # Issue 1882: Needs --disable_privacy support.
 DoubleToStringAsExponentialTest: Fail # fails due to -0.0.
 # Once the -0.0 in DoubleToStringAsFixedTest is fixed it will probably need to
 # be moved to a
 # [ $compiler == frog ]
 # section.
 DoubleToStringAsFixedTest: Fail # fails due to -0.0 and due to rounding in constant propagation.
 DoubleToStringAsPrecisionTest: Fail # fails due to -0.0.
 ExtendTypeParameterNegativeTest: Skip # Issue 886
 ExtendTypeParameter2NegativeTest: Skip # Issue 886
@@ skipping 231 matching lines @@
 [ $compiler == frog && $mode == debug ]
 ConstructorRedirect1NegativeTest: Skip # Undiagnosed infinite loop.
 ConstructorRedirect2NegativeTest: Skip # Undiagnosed infinite loop.
 
 [ $arch == simarm ]
 *: Skip
 
 [ $arch == arm ]
 *: Skip