RFC: Start refactoring to provide more than a single backend.

lib/compiler/implementation/native_emitter.dart

Index: lib/compiler/implementation/native_emitter.dart
diff --git a/lib/compiler/implementation/native_emitter.dart b/lib/compiler/implementation/native_emitter.dart
index e4e977b7b94817f843328fa7ae5e7806539646f2..c11d25fe1d395d54412d21f09ebb434244e69579 100644
--- a/lib/compiler/implementation/native_emitter.dart
+++ b/lib/compiler/implementation/native_emitter.dart
@@ -85,7 +85,7 @@ class NativeEmitter {
     for (Element member in classElement.members) {
       if (member.isInstanceMember()) {
         bool needGettersAndSetters = true;
-        compiler.emitter.addInstanceMember(
+        compiler.backend.emitter.addInstanceMember(
             member, needGettersAndSetters, defineInstanceMember);
       }
     }
@@ -132,12 +132,12 @@ class NativeEmitter {
     for (Element member in classElement.members) {
       if (member.isInstanceMember()) {
         bool needGettersAndSetters = true;
-        compiler.emitter.addInstanceMember(
+        compiler.backend.emitter.addInstanceMember(
           member, needGettersAndSetters, defineInstanceMember);
       }
     }
 
-    compiler.emitter.generateTypeTests(classElement, (Element other) {
+    compiler.backend.emitter.generateTypeTests(classElement, (Element other) {
       assert(requiresNativeIsCheck(other));
       defineInstanceMember(compiler.namer.operatorIs(other),
                            "function() { return true; }");