Extract CodegenImpactTransformer from ImpactTransformer

pkg/compiler/lib/src/common/backend_api.dart

Index: pkg/compiler/lib/src/common/backend_api.dart
diff --git a/pkg/compiler/lib/src/common/backend_api.dart b/pkg/compiler/lib/src/common/backend_api.dart
index c2ff777ad40e0f1f91e331c80dd5cf2069c82f5a..5c21ada00b2a966c3df062919b16807162ab9492 100644
--- a/pkg/compiler/lib/src/common/backend_api.dart
+++ b/pkg/compiler/lib/src/common/backend_api.dart
@@ -37,7 +37,7 @@ abstract class ForeignResolver {
   ResolutionDartType resolveTypeFromString(Node node, String typeName);
 }
 
-/// Backend transformation methods for the world impacts.
+/// Backend transformation for resolution world impacts.

[Siggi Cherem (dart-lang), 2017/03/14 05:33:01]

you might want to define what a impact transformation is (e.g. "it process
target-agnostic impacts and appends extra impact data that is backend/target
specific, for example: if certain feature is used that requires some helper code
from the backend libraries, this will be included by the impact transformer"...)

[Johnni Winther, 2017/03/15 13:11:50]

Done.

 class ImpactTransformer {
   /// Transform the [ResolutionImpact] into a [WorldImpact] adding the
   /// backend dependencies for features used in [worldImpact].
@@ -45,12 +45,6 @@ class ImpactTransformer {
       ResolutionEnqueuer enqueuer, ResolutionImpact worldImpact) {
     return worldImpact;
   }
-
-  /// Transform the [CodegenImpact] into a [WorldImpact] adding the
-  /// backend dependencies for features used in [worldImpact].
-  WorldImpact transformCodegenImpact(CodegenImpact worldImpact) {
-    return worldImpact;
-  }
 }
 
 /// Interface for serialization of backend specific data.