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

tests/language/language-leg.status

Index: tests/language/language-leg.status
diff --git a/tests/language/language-leg.status b/tests/language/language-leg.status
index 93739d009a837bd1f9913ecddca851380a640699..60db2031938ba0c1802801c74687ca4e9d7b77c4 100644
--- a/tests/language/language-leg.status
+++ b/tests/language/language-leg.status
@@ -9,7 +9,6 @@
 [ $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.
@@ -28,8 +27,8 @@ 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.
@@ -40,7 +39,6 @@ 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.