Move native and js interop properties from the element model to the JS backend

pkg/compiler/lib/src/native/ssa.dart

 // Copyright (c) 2014, 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.
 
 part of native;
 
 final RegExp nativeRedirectionRegExp = new RegExp(r'^[a-zA-Z][a-zA-Z_$0-9]*$');
 
 void handleSsaNative(SsaBuilder builder, Expression nativeBody) {
   Compiler compiler = builder.compiler;
@@ skipping 17 matching lines @@
   }
 
   // Check which pattern this native method follows:
   // 1) foo() native;
   //      hasBody = false
   // 2) foo() native "bar";
   //      No longer supported, this is now done with @JSName('foo') and case 1.
   // 3) foo() native "return 42";
   //      hasBody = true
   bool hasBody = false;
-  assert(element.isNative);
-  String nativeMethodName = element.fixedBackendName;
+  assert(backend.isNative(element));
+  String nativeMethodName = backend.getFixedBackendName(element);
   if (nativeBody != null) {
     LiteralString jsCode = nativeBody.asLiteralString();
     String str = jsCode.dartString.slowToString();
     if (nativeRedirectionRegExp.hasMatch(str)) {
       reporter.internalError(
           nativeBody, "Deprecated syntax, use @JSName('name') instead.");
     }
     hasBody = true;
   }
 
@@ skipping 56 matching lines @@
     LiteralString jsCode = nativeBody.asLiteralString();
     builder.push(new HForeignCode.statement(
         js.js.statementTemplateYielding(
             new js.LiteralStatement(jsCode.dartString.slowToString())),
         <HInstruction>[],
         new SideEffects(),
         null,
         backend.dynamicType));
   }
 }