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..4718693f0bddeb3519f74f474db37a0a546d0fb4 100644
--- a/lib/compiler/implementation/native_emitter.dart
+++ b/lib/compiler/implementation/native_emitter.dart
@@ -4,7 +4,7 @@
 
 class NativeEmitter {
 
-  Compiler compiler;
+  Emitter emitter;
   StringBuffer nativeBuffer;
 
   // Classes that participate in dynamic dispatch. These are the
@@ -30,7 +30,7 @@ class NativeEmitter {
   // implementation.
   Set<FunctionElement> nativeMethods;
 
-  NativeEmitter(this.compiler)
+  NativeEmitter(this.emitter)
       : classesWithDynamicDispatch = new Set<ClassElement>(),
         nativeClasses = new Set<ClassElement>(),
         subtypes = new Map<ClassElement, List<ClassElement>>(),
@@ -39,6 +39,8 @@ class NativeEmitter {
         nativeMethods = new Set<FunctionElement>(),
         nativeBuffer = new StringBuffer();
 
+  Compiler get compiler() => emitter.compiler;
+
   String get dynamicName() {
     Element element = compiler.findHelper(
         const SourceString('dynamicFunction'));
@@ -85,7 +87,7 @@ class NativeEmitter {
     for (Element member in classElement.members) {
       if (member.isInstanceMember()) {
         bool needGettersAndSetters = true;
-        compiler.emitter.addInstanceMember(
+        emitter.addInstanceMember(
             member, needGettersAndSetters, defineInstanceMember);
       }
     }
@@ -132,12 +134,12 @@ class NativeEmitter {
     for (Element member in classElement.members) {
       if (member.isInstanceMember()) {
         bool needGettersAndSetters = true;
-        compiler.emitter.addInstanceMember(
+        emitter.addInstanceMember(
           member, needGettersAndSetters, defineInstanceMember);
       }
     }
 
-    compiler.emitter.generateTypeTests(classElement, (Element other) {
+    emitter.generateTypeTests(classElement, (Element other) {
       assert(requiresNativeIsCheck(other));
       defineInstanceMember(compiler.namer.operatorIs(other),
                            "function() { return true; }");