Fix some bugs regarding native fields.

dart/sdk/lib/_internal/compiler/implementation/compiler.dart

Index: dart/sdk/lib/_internal/compiler/implementation/compiler.dart
diff --git a/dart/sdk/lib/_internal/compiler/implementation/compiler.dart b/dart/sdk/lib/_internal/compiler/implementation/compiler.dart
index c3012714409a6e53255047ea012895530e65dac8..47e44e73bf95d64fa429537d0333faa515be4d8d 100644
--- a/dart/sdk/lib/_internal/compiler/implementation/compiler.dart
+++ b/dart/sdk/lib/_internal/compiler/implementation/compiler.dart
@@ -680,7 +680,7 @@ abstract class Compiler implements DiagnosticListener {
       tracer.close();
       totalCompileTime.stop();
     }
-    return true;
+    return !compilationFailed;
   }
 
   bool hasIsolateSupport() => isolateLibrary != null;
@@ -955,6 +955,10 @@ abstract class Compiler implements DiagnosticListener {
     backend.assembleProgram();
 
     checkQueues();
+
+    if (compilationFailed) {
+      assembledCode = null; // Signals failure.
+    }
   }
 
   void fullyEnqueueLibrary(LibraryElement library, Enqueuer world) {