Revert "Reduce use of Element in optimize.dart"

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

Index: pkg/compiler/lib/src/native/ssa.dart
diff --git a/pkg/compiler/lib/src/native/ssa.dart b/pkg/compiler/lib/src/native/ssa.dart
index fe7d0983249a2cb90f2a5cc45d9d8c715632950a..d72558d2c4bf987d851d9ca2404dcae31ff146c5 100644
--- a/pkg/compiler/lib/src/native/ssa.dart
+++ b/pkg/compiler/lib/src/native/ssa.dart
@@ -19,7 +19,7 @@ final RegExp nativeRedirectionRegExp = new RegExp(r'^[a-zA-Z][a-zA-Z_$0-9]*$');
 
 void handleSsaNative(SsaBuilder builder, Expression nativeBody) {
   Compiler compiler = builder.compiler;
-  MethodElement element = builder.target;
+  FunctionElement element = builder.target;
   NativeEmitter nativeEmitter = builder.nativeEmitter;
   JavaScriptBackend backend = builder.backend;
   DiagnosticReporter reporter = compiler.reporter;