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

lib/compiler/implementation/native_handler.dart

Index: lib/compiler/implementation/native_handler.dart
diff --git a/lib/compiler/implementation/native_handler.dart b/lib/compiler/implementation/native_handler.dart
index 7b392fa02ee9f9c69310ec78d7cb2b573174dab2..dd72d700473f62201b10385dbd7441c370f04489 100644
--- a/lib/compiler/implementation/native_handler.dart
+++ b/lib/compiler/implementation/native_handler.dart
@@ -53,7 +53,7 @@ void processNativeClassesInLibrary(Compiler compiler,
         // Add the information that this class is a subtype of
         // its supertypes. The code emitter and the ssa builder use that
         // information.
-        NativeEmitter emitter = compiler.emitter.nativeEmitter;
+        NativeEmitter emitter = compiler.backend.emitter.nativeEmitter;
         addSubtypes(classElement, emitter);
       }
     }
@@ -195,7 +195,7 @@ void handleSsaNative(SsaBuilder builder, Send node) {
   Compiler compiler = builder.compiler;
   FunctionElement element = builder.work.element;
   element.setNative();
-  NativeEmitter nativeEmitter = compiler.emitter.nativeEmitter;
+  NativeEmitter nativeEmitter = compiler.backend.emitter.nativeEmitter;
   // If what we're compiling is a getter named 'typeName' and the native
   // class is named 'DOMType', we generate a call to the typeNameOf
   // function attached on the isolate.
@@ -247,7 +247,7 @@ void handleSsaNative(SsaBuilder builder, Send node) {
   }
 
   if (!hasBody) {
-    compiler.emitter.nativeEmitter.nativeMethods.add(element);
+    compiler.backend.emitter.nativeEmitter.nativeMethods.add(element);
   }
 
   FunctionSignature parameters = element.computeSignature(builder.compiler);