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

tests/language/language-leg.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.
 
 [ $compiler == dart2js && $checked ]
 *: Skip
 
 
 [ $compiler == dart2js]
 AdjacentConstStringLiteralsTest: Pass # Not recognizing 'const' constructor call.
 CompileTimeConstant8Test: Fail # We don't take the generic type into account yet.
-CompileTimeConstantBTest: Fail # We don't handle constant map literals with __proto__ key yet.
 
 
 # Compilation errors.
 CTConstTest: Fail # map not implemented
 CallOperatorTest: Fail # Unexpected token 'call'
 CharEscapeTest: Fail # Unhandled non-BMP character: U+10000
 ConstObjectsAreImmutableTest: Fail # map not implemented
 Constructor6Test: Fail # Closures inside initializers not implemented.
 DefaultFactoryLibraryTest: Fail # lib is not a type
 DynamicTest: Fail # cannot resolve type F1
 Factory3Test: Fail # Handling of compile-time constants.
 FinalSyntaxTest/none: Fail # Incorrect compile-time constant handling.
 FunctionLiterals2Test: Fail # Closures inside initializers not implemented.
 FunctionSyntaxTest: Fail # Closures inside initializers not implemented.
 FunctionTypeAlias2Test: Fail # cannot resolve type f1
 FunctionTypeAlias3Test: Fail # cannot resolve type F
 FunctionTypeAlias4Test: Fail # cannot resolve type F
 FunctionTypeAliasTest: Fail # cannot resolve type Fun
-FunctionTypeParameter2Test: Fail # Internal Error: expected expected optional parameters
-FunctionTypeParameterTest: Fail # Internal Error: expected expected optional parameters
+FunctionTypeParameter2Test: Fail # Internal Error: expected optional parameters
+FunctionTypeParameterTest: Fail # Internal Error: expected optional parameters
 GenericInstanceofTest: Fail # cannot resolve type T
 GenericTest: Fail # cannot resolve type T
 GetSetSyntaxTest/none: Fail # Parsing of pseudo keywords.
 GettersSettersTest: Fail # Internal Error: SsaBuilder.visitIdentifier on non-this
 ImplicitScopeTest: Fail # duplicate definition of a="bar"
 LabelTest: Fail # switch cases are not implemented
 LibraryPrefixesTest: Fail # other is not a type
 LocalFunctionTest: Fail # duplicate definition of f(var n)=> n*n-1
 ManyGenericInstanceofTest: Fail # cannot resolve type T
 MapLiteral2Test: Fail # expected a constant string
-MapLiteral3Test: Fail # CL on its way (const { 'a': 3, 'a': 4 } not treated correctly.
 MapLiteral4Test: Fail # map not implemented
 MethodBindingTest: Fail # Internal Error: SsaBuilder.visitIdentifier on non-this
 MethodNameTest: Fail # Parsing of pseudo keywords.
 MethodOverrideTest: Fail # cannot resolve type GetKeysFunctionType
 NamedParameters2Test: Fail # Unimplemented non-matching static call
 NamedParameters3Test: Fail # Unimplemented non-matching static call
 NamedParameters4Test: Fail # Unimplemented non-matching static call
 NamedParametersTypeTest: Fail # Internal Error: Cannot find value
 NamingTest: Fail # Internal Error: Cannot find value
 NanInfinityTest: Fail # CompileTimeConstantEvaluator not implemented
@@ skipping 157 matching lines @@
 
 
 RegExp3Test: Fail, OK # Expects exception from const constructor.
 
 
 ListTest: Fail, OK # Obsolete test uses List.copyFrom that was removed on 2011-10-31.
 
 
 [ $compiler == dart2js && $mode == release ]
 AssignTopMethodNegativeTest: Crash