Element model cleanup + prepare for easier reimplementation.

pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart

Index: pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart
diff --git a/pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart b/pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart
index 6b78f6fffcf8e96d6d51e3e1766e41951f0ef459..7a6382a56b67564c9e51d646846a82cb782d53b0 100644
--- a/pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart
+++ b/pkg/compiler/lib/src/cps_ir/cps_ir_builder_task.dart
@@ -764,7 +764,7 @@ abstract class IrBuilderVisitor extends ast.Visitor<ir.Primitive>
       MethodElement function,
       _) {
     // TODO(karlklose): support foreign functions.
-    if (function.isForeign(compiler.backend)) {
+    if (compiler.backend.isForeign(function)) {
       return giveup(node, 'handleStaticFunctionGet: foreign: $function');
     }
     return irBuilder.buildStaticFunctionGet(function);
@@ -1113,7 +1113,7 @@ abstract class IrBuilderVisitor extends ast.Visitor<ir.Primitive>
       CallStructure callStructure,
       _) {
     // TODO(karlklose): support foreign functions.
-    if (function.isForeign(compiler.backend)) {
+    if (compiler.backend.isForeign(function)) {
       return giveup(node, 'handleStaticFunctionInvoke: foreign: $function');
     }
     return irBuilder.buildStaticFunctionInvocation(function, callStructure,
@@ -1139,7 +1139,7 @@ abstract class IrBuilderVisitor extends ast.Visitor<ir.Primitive>
       ast.NodeList arguments,
       CallStructure callStructure,
       _) {
-    if (getter.isForeign(compiler.backend)) {
+    if (compiler.backend.isForeign(getter)) {
       return giveup(node, 'handleStaticGetterInvoke: foreign: $getter');
     }
     ir.Primitive target = irBuilder.buildStaticGetterGet(getter);